Federal Motor Vehicle Safety Standards; Tire Pressure Monitoring Systems; Controls and Displays

Federal RegisterJun 5, 2002

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Parts 571 and 590

[Docket No. NHTSA 2000-8572]

RIN 2127-AI33

Federal Motor Vehicle Safety Standards; Tire Pressure Monitoring Systems; Controls and Displays

AGENCY:

National Highway Traffic Safety Administration (NHTSA), Department of Transportation (DOT).

ACTION:

Final rule.

SUMMARY:

In response to a mandate in the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act of 2000, this agency is issuing a two-part final rule.

The first part is contained in this document. It establishes a new Federal Motor Vehicle Safety Standard that requires the installation of tire pressure monitoring systems (TPMSs) that warn the driver when a tire is significantly under-inflated. The standard applies to passenger cars, trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle.

This document establishes two compliance options for the short-term, for the period between November 1, 2003, and October 31, 2006. Under the first compliance option, a vehicle's TPMS must warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, has fallen to 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. Under the second compliance option, a vehicle's TPMS must warn the driver when the pressure in any single tire has fallen to 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. Compliance with the options would be phased in during that period by increasing percentages of production.

The second part of this final rule will be issued by March 1, 2005, and will establish performance requirements for the long-term,

i.e.,

for the period beginning on November 1, 2006. In the meantime, the agency will leave the rulemaking docket open for the submission of new data and analyses concerning the performance of TPMSs. The agency also will conduct a study comparing the tire pressures of vehicles without any TPMS to the pressures of vehicles with TPMSs, especially TPMSs that do not comply with the four-tire, 25 percent compliance option.

Based on the record now before the agency, NHTSA tentatively believes that the four-tire, 25 percent option would best meet the mandate in the TREAD Act. However, it is possible that the agency may obtain or receive new information that is sufficient to justify a continuation of the options established by this first part of this rule, or the adoption of some other alternative.

DATES:

This final rule is effective August 5, 2002. Under the rule, vehicles will be required to comply with the requirements of the standard according to a phase-in beginning on November 1, 2003. If you wish to submit a petition for reconsideration of this rule, your petition must be received by July 22, 2002.

ADDRESSES:

Petitions for reconsideration should refer to the docket number and be submitted to: Administrator, Room 5220, National Highway Traffic Safety Administration, 400 Seventh Street, SW, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT:

For technical and other non-legal issues, you may call Mr. George Soodoo or Mr. Joseph Scott, Office of Crash Avoidance Standards (Telephone: 202-366-2720) (Fax: 202-366-4329).

For legal issues, you may call Mr. Dion Casey, Office of Chief Counsel (Telephone: 202-366-2992) (Fax: 202-366-3820).

You may send mail to these officials at National Highway Traffic Safety Administration, 400 Seventh Street, SW, Washington, DC 20590.

You may call Docket Management at 202-366-9324. You may visit the Docket on the plaza level at 400 Seventh Street, SW, Washington, DC, from 10:00 a.m. to 5:00 p.m., Monday through Friday.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary

A. Highlights of the Notice of Proposed Rulemaking

B. Highlights of the Preliminary Determination About the Final Rule

C. OMB Return Letter

D. Highlights of the Final Rule

1. Part One—Phase-in (November 2003 through October 2006)

2. Part Two—November 2006 and Thereafter

E. Summary Comparison of the Preliminary Determination and the Final Rule

II. Background

A. The Transportation Recall Enhancement, Accountability, and Documentation Act

B. Previous Rulemaking on Tire Pressure Monitoring Systems

C. Summary of the Notice of Proposed Rulemaking

D. Summary of Public Comments on Notice

1. Vehicles Covered

2. Phase-In Options and Long-Term Requirements

a. Definition of “Significantly Under-Inflated”

b. Number of Tires Monitored

3. Lead Time

4. Reliability

5. Costs and Benefits Estimates

E. Submission of Draft Final Rule to OMB

F. OMB Return Letter

G. Public Comments on OMB's Return Letter

H. Congressional Hearing

III. Safety Problem

A. Infrequent Driver Monitoring of Tire Pressure

B. Loss of Tire Pressure Due to Natural and Other Causes

C. Percentage of Motor Vehicles with Under-Inflated Tires

D. Consequences of Under-Inflation of Tires

1. Reduced Vehicle Safety—Tire Failures and Increases in Stopping Distance

2. Reduced Tread Life

3. Reduced Fuel Economy

IV. Tire Pressure Monitoring Systems

A. Indirect TPMSs

B. Direct TPMSs

C. Hybrid TPMSs

V. Summary of Preliminary Determination About the Final Rule

A. Alternative Long-Term Requirements Analyzed in Making Preliminary Determination

B. Phase-In and Long-Term Requirements

VI. Response to Issues Raised in OMB Return Letter About Preliminary Determination

A. Criteria for Selecting the Long-Term Requirement

1. Tire Safety and Overall Vehicle Safety

2. Statutory Mandate

B. Relative Ability of Direct and Current Indirect TPMSs to Detect Under-Inflation

C. Analysis of a Fourth Alternative Long-Term Requirement: One-Tire, 30 Percent Under-Inflation Detection

D. Impact of One-Tire, 30 Percent Alternative on Installation Rate of ABS

E. Overall Safety Effects of ABS

F. Technical Foundation for NHTSA's Safety Benefit Analyses

VII. The Final Rule

A. Decision to Issue Two-Part Final Rule

B. Part One of the Final Rule—November 2003 through October 2006

1. Summary

2. Congressional Intent

3. Vehicles Covered

4. Phase-In Options and Requirements

a. Alternatives Considered

i. Threshold Level of Under-Inflation

ii. Number of Tires Monitored

b. Option One: Four Tires, 25 Percent Under-Inflation

c. Option Two: One Tire, 30 Percent Under-Inflation

d. Special Written Instructions for Option Two TPMSs

5. Other Requirements

a. Time Frame for Telltale Illumination

b. Duration of Warning

c. Temporary Disablement

d. System Calibration

e. Replacement Tires

f. Monitoring of Spare Tire

g. Temperature Compensation

h. Low Tire Pressure Warning Telltale

i. Color

ii. Symbol

iii. Self-Check

i. General Written Instructions for All TPMSs

j. Test Conditions

k. Test Procedures

6. Lead Time

C. Study of Effects of TPMSs That Do Not Meet a Four-Tire, 25 Percent Under-Inflation Requirement

1. Effect on Tire Pressure

2. Effect on Number of Significantly Under-Inflated Tires

D. Part Two of the Final Rule—November 2006 and Thereafter

VIII. Benefits

A. Tire Safety Benefits

1. Skidding/Loss of Control

2. Stopping Distance

3. Flat Tires and Blowouts

4. Unquantified Benefits

B. Non-Tire Safety Benefits

C. Total Quantified Safety Benefits

D. Economic Benefits

1. Fuel Economy

2. Tread Life

IX. Costs

A. Indirect TPMSs

B. Direct TPMSs

C. Hybrid TPMSs

D. Vehicle Cost

E. Maintenance Costs

F. Testing Costs

G. Unquantified Costs

H. ABS Costs

I. Net Costs and Costs Per Equivalent Life Saved

X. Rulemaking Analyses and Notices

I. Executive Summary

A. Highlights of the Notice of Proposed Rulemaking

NHTSA initiated this rulemaking with the publication of a Notice of Proposed Rulemaking (NPRM)(66 FR 38982, Docket No. NHTSA-2000-8572) on July 26, 2001. The NPRM proposed to require passenger cars, light trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle, to be equipped with a tire pressure monitoring system (TPMS).

The agency sought comment on two alternative sets of performance requirements for TPMSs and proposed adopting one of them in the final rule. The first alternative would have required that the driver be warned when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, had fallen to 20 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the vehicle's tires (the placard pressure), or a minimum level of pressure specified in the standard, whichever was higher. (This alternative is referred to below as the four-tire, 20 percent alternative.) The second alternative would have required that the driver be warned when the pressure in any single tire or in each tire in any combination of tires, up to a total of three tires, had fallen to 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever was higher. (This alternative is referred to below as the three-tire, 25 percent alternative.) The minimum levels of pressure were the same in both proposed alternatives. The adoption of four-tire, 20 percent alternative would have required that drivers be warned of under-inflation sooner and in a greater array of circumstances. It would also have narrowed the range of technologies that manufacturers could use to comply with the new standard.

There are two types of TPMSs currently available, direct TPMSs and indirect TPMSs. Direct TPMSs have a tire pressure sensor in each tire. The sensors transmit pressure information to a receiver. Indirect TPMSs do not have tire pressure sensors. Current indirect TPMSs rely on the wheel speed sensors in an anti-lock braking system (ABS) to detect and compare differences in the rotational speed of a vehicle's wheels. Those differences correlate to differences in tire pressure because decreases in tire pressure cause decreases in tire diameter that, in turn, cause increases in wheel speed.

To meet the four-tire, 20 percent alternative, vehicle manufacturers likely would have had to use direct TPMSs because even improved indirect systems would not likely be able to detect loss of pressure until pressure has fallen 25 percent and could not detect all combinations of significantly under-inflated tires. To meet the three-tire, 25 percent alternative, vehicle manufacturers would have been able to install either direct TPMSs or improved indirect TPMSs, but not current indirect TPMSs.

B. Highlights of the Preliminary Determination About the Final Rule

NHTSA preliminarily determined to issue a final rule that would have specified a four-year phase-in schedule

and allowed compliance with either of two options during the phase-in, i.e., between November 1, 2003 and October 31, 2006. Under the first option, a vehicle's TPMS would have had to warn the driver when the pressure in one or more of the vehicle's tires, up to a total of four tires, was 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. (This option is referred to below as the four-tire, 25 percent option.) Under the second option, a vehicle's TPMS would have had to warn the driver when the pressure in any one of the vehicle's tires was 30 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. (This option is referred to below as the one-tire, 30 percent option.) The minimum levels of pressure specified in the standard were the same for both compliance options.

The phase-in schedule was as follows: 10 percent of a manufacturer's affected vehicles would have had to comply with either compliance option in the first year; 35 percent in the second year; and 65 percent in the third year. In the fourth year, 100 percent of a manufacturer's affected vehicles would have had to comply with the long-term requirements, i.e., the four-tire, 25 percent compliance option.

After the phase-in,

i.e.,

after October 31, 2006, the second option would have been terminated, and the provisions of the first option would have become mandatory for all new vehicles. Thus, all vehicles would have been required to meet a four-tire, 25 percent requirement.

C. OMB Return Letter

After reviewing the draft final rule, OMB returned it to NHTSA for reconsideration, with a letter explaining its reasons for doing so, on February 12, 2002. In the letter, OMB stated its belief that the draft final rule and accompanying regulatory impact analysis did not adequately demonstrate that the agency had selected the best available method of improving overall vehicle safety.

D. Highlights of the Final Rule

In response to the OMB return letter, the agency has decided to divide the final rule into two parts. The first part is contained in this document, which establishes requirements for vehicles manufactured during the first three years,

i.e.,

between November 1, 2003, and October 31, 2006, and phases them in by increasing percentages of production. The second part will establish requirements for vehicles manufactured on or after November 1, 2006.

The agency has divided the final rule into two parts because it has decided to

defer its decision as to which long-term performance requirements for TPMS would best satisfy the mandate of the TREAD Act. This deferral will allow the agency's consideration of additional data on the effect and performance of TPMSs. From the beginning, the agency has sought to comply with the mandate and safety goals of the TREAD Act in a way that encourages innovation and allows a range of technologies to the extent consistent with providing drivers with sufficient warning of low tire pressure under a broad variety of the reasonably foreseeable circumstances in which tires become under-inflated.

1. Part One—Phase-in (November 2003 through October 2006)

NHTSA has decided to require vehicle manufacturers to equip their light vehicles (

i.e.,

those with a gross vehicle weight rating (GVWR) of 10,000 lbs. or less) with TPMSs and to give them the option for complying with either of two sets of performance requirements during the period covered by the first part of the final rule,

i.e.,

from November 1, 2003 to October 31, 2006. The options are the same as those in the preliminary determination about the final rule.

Under the first set or compliance option, the vehicle's TPMS will be required to warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, is 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. Under the second compliance option, the vehicle's TPMS will be required to warn the driver when the pressure in any single tire is 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher.

The two compliance options are outgrowths of the alternative sets of requirements proposed in the NPRM. In response to comments confirming that current indirect TPMSs cannot meet the proposed three-tire, 25 percent under-inflation requirements, and in order to allow those systems to be used during the phase-in, the agency is adopting requirements for detection of one-tire, 30 percent under-inflation as the first option. For the second option, the agency is adopting requirements for detection of 4-tire, 25 percent under-inflation. Adopting those requirements, instead of the proposed requirements for four-tire, 20 percent under-inflation, will permit manufacturers to use either direct TPMSs or hybrid TPMSs,

i.e.,

TPMSs that combine direct and indirect TPMS technologies. One TPMS supplier indicated the potential for developing and producing hybrid systems, although it also indicated that it did not currently have plans for doing so. The agency believes that the difference in benefits between TPMSs meeting four-tire, 20 percent requirements and TPMSs meeting four-tire, 25 percent requirements should not be substantial.

The minimum levels of pressure are the same for both compliance options.

To facilitate compliance with the options, the rule phases them in by increasing percentages of production. Ten percent of a vehicle manufacturer's light vehicles will be required to comply with either compliance option during the first year (November 1, 2003 to October 31, 2004), 35 percent during the second year (November 1, 2004 to October 31, 2005), and 65 percent during the third year (November 1, 2005 to October 31, 2006). These percentages are the same as those in the preliminary determination about the final rule. The agency is allowing carry-forward credits for vehicles that are manufactured during the phase-in and are equipped with TPMSs that comply with the four-tire, 25 percent option. It is not allowing credits for TPMSs complying with the other option for the same reason that the agency is requiring manufacturers to provide consumers with information about the performance limitations of those systems.

The combination of the two compliance options and the phase-in will allow manufacturers to continue to use current indirect TPMSs during that period and ease the implementation of the TPMS standard. The agency notes that, for vehicles already equipped with ABS, the installation of a current indirect TPMS is the least expensive way of complying with a TPMS standard. The compliance options and phase-in will also give manufacturers the flexibility needed to innovate and improve the performance of their TPMSs. This flexibility will improve the chances that ways can be found to improve the detection of under-inflation as well as reduce the costs of doing so.

The owner's manual for vehicles certified to either compliance option will be required to include written information explaining the purpose of the low tire pressure warning telltale, the potential consequences of driving on significantly under-inflated tires, the meaning of the telltale when it is illuminated, and the actions that drivers should take when the telltale is illuminated. In addition, the owner's manual in vehicles certified to the one-tire, 30 percent option will be required to include information on the inherent performance limitations of current indirect TPMSs because the agency anticipates that most indirect TPMSs installed to comply with that option will exhibit those limitations and because a vehicle owner survey indicates that a significant majority of drivers would be less concerned, to either a great extent or a very great extent, with routinely maintaining the pressure of their tires if their vehicle were equipped with a TPMS. Under both compliance options, the TPMS will be required to have a low tire pressure-warning telltale (yellow).

2. Part Two—November 2006 and Thereafter

Beginning November 1, 2006, all passenger cars and light trucks, multipurpose passenger vehicles, and buses under 10,000 pounds GVWR will be required to comply with the requirements in the second part of this final rule. The agency will publish the second part of this final rule by March 1, 2005, in order to give manufacturers sufficient lead time before vehicles must meet the requirements.

In anticipation of making the decision in part two of this final rule about the long-term requirements, the agency will leave the rulemaking docket open for the submission of new data and analyses. The agency also will conduct a study comparing the tire pressures of vehicles without any TPMS to the pressures of vehicles with TPMSs that do not comply with the four-tire, 25 percent compliance option. When completed, it will be placed in the docket for public examination. After consideration of the record compiled to this date, as supplemented by the results of the tire pressure study and any other new information submitted to the agency, NHTSA will issue the second part of this rule by March 1, 2005.

Based on the record now before the agency, NHTSA tentatively believes that the four-tire, 25 percent option would best meet the mandate in the TREAD Act. However, it is possible that the agency may obtain or receive new information that is sufficient to justify a continuation of the compliance options established by the first part of this final rule, or the adoption of some other alternative.

E. Summary Comparison of the Preliminary Determination and the Final Rule

The primary difference between the preliminary determination and the final rule is one of timing, instead of substance. The options and percentages of production for the phase-in years are unchanged.

The final rule does differ from the preliminary determination in the timing of the agency's decision about the performance requirements for the years following the phase-in period.

The final rule does require that additional information be placed in the vehicle's owner manual.

Summary Comparison of the Preliminary Determination and the Final Rule

Preliminary determination

Final rule

Application

Passenger cars, trucks, multipurpose passenger vehicles, and buses with a GVWR of 10,000 pounds or less, except those vehicles with dual wheels on an axle

Same.

Short-term (11/1/03—10/31/06):

Compliance Options

Option 1: TPMS must warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, has fallen to 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher

Same.

Option 2: TPMS must warn the driver when the pressure in any single tire has fallen to 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher

Same.

Phase-in Schedule

10% of a vehicle manufacturer's light vehicles will be required to comply with either compliance option during the first year (November 1, 2003 to October 31, 2004), 35 percent during the second year (November 1, 2004 to October 31, 2005), and 65 percent during the third year (November 1, 2005 to October 31, 2006)

Same.

Long-term (11/1/06 & thereafter):

Performance Requirements

TPMS must warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, has fallen to 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher

Decision to be made by March 1, 2005.

II. Background

A. The Transportation Recall Enhancement, Accountability, and Documentation Act

Congress enacted the TREAD Act on November 1, 2000.

Section 13 of the TREAD Act mandated the completion of “a rulemaking for a regulation to require a warning system in new motor vehicles to indicate to the operator when a tire is significantly under inflated” within one year of the TREAD Act's enactment. Section 13 also requires the regulation to take effect within two years of the completion of the rulemaking.

Public Law 106-414.

Tri-Level Study of the Causes of Traffic Accidents, Treat, J.R., et al. (1979) (Contract No. DOT HS 034-3-535), DOT HS 805 099, Washington, DC: U.S. Department of Transportation, National Highway Traffic Safety Administration.

B. Previous Rulemaking on Tire Pressure Monitoring Systems

NHTSA first considered requiring a “low tire pressure warning” device in 1970. However, the agency determined that the only warning device available at that time was an in-vehicle indicator whose cost was too high.

During the 1970s, several manufacturers developed inexpensive, on-tire warning devices. In addition, the price of in-vehicle warning devices dropped significantly.

As a result, on January 26, 1981, NHTSA published an Advanced Notice of Proposed Rulemaking (ANPRM) soliciting public comment on whether the agency should propose a new Federal motor vehicle safety standard requiring each new motor vehicle to have a low tire pressure warning device which would “warn the driver when the tire pressure in any of the vehicle's tires was significantly below the recommended operating levels.” (46 FR 8062.)

NHTSA noted in the ANPRM that under-inflation increases the rolling resistance of tires and, correspondingly, decreases the fuel economy of vehicles. Research data at the time indicated that the under-inflation of a vehicle's radial tires by 10 pounds per square inch (psi) reduced the fuel economy of the vehicle by 3 percent. Because of the worldwide oil shortages in the late 1970s and early 1980s, NHTSA was interested in finding ways to increase the fuel economy of passenger vehicles (i.e., passenger cars and multipurpose passenger vehicles). Since surveys by the agency showed that about 50 percent of passenger car tires and 13 percent of truck tires were operated at pressures below the vehicle manufacturer's recommended (placard) pressure, the agency believed that low tire pressure warning devices would encourage drivers to maintain their tires at the proper inflation level, thus maximizing their vehicles' fuel economy.

Moreover, a 1977 study by Indiana University concluded that under-inflated tires were a probable cause of 1.4 percent of all motor vehicle crashes.

Based on that figure, and the approximately 18.3 million motor vehicle crashes then occurring annually in the United States, the agency suggested that under-inflated tires were probably responsible for 260,000 crashes each year (1.4 percent x 18.3 million crashes).

In the ANPRM, NHTSA sought answers from the public to several questions, including:

(1) What tire pressure level should trigger the warning device?

(2) Should the agency specify the type of warning device (i.e., on-tire or in-vehicle) to be used?

(3) What would it cost to produce and install an on-tire or in-vehicle warning device?

(4) What is the fuel saving potential of low tire pressure warning devices?

(5) What studies have been performed which would show cause and effect relationships between low tire pressure and auto crashes?

(6) What would be the costs and benefits of a program to educate the public on the benefits of maintaining proper tire pressure?

NHTSA terminated the rulemaking on August 31, 1981, because public comments indicated that the low tire pressure warning devices available at the time either had not been proven to be accurate and reliable (on-tire devices) or were too expensive (in-vehicle devices). (46 FR 43721.) The comments indicated that in-vehicle warning devices had been proven to be accurate and reliable, but would have had a retail cost of $200 (in 1981 dollars) per vehicle. NHTSA stated, “Such a cost increase cannot be justified by the potential benefits, although those benefits might be significant.” (46 FR 43721.) The comments also indicated that on-tire warning devices cost only about $5 (in 1981 dollars), but they had not been developed to the point where they were accurate and reliable enough to be required. The comments also suggested that on-tire warning devices were subject to damage by road hazards, such as ice and mud, as well as scuffing at curbs. Despite terminating the rulemaking, the agency stated that it still believed that “[m]aintaining proper tire inflation pressure results in direct savings to drivers in terms of better gas mileage and longer tire life, as well as offering increased safety.” (46 FR 43721.)

C. Summary of the Notice of Proposed Rulemaking

On July 26, 2001, the agency published the NPRM proposing to establish a standard for TPMSs pursuant to section 13 of the TREAD Act. (66 FR 38982.) The agency proposed two alternative versions of the standard.

The two alternatives differed in two important respects: in how they defined “significantly under-inflated,” and in the number of significantly under-inflated tires that they would be required to be able to detect at any one time. The first alternative (four tires, 20 percent) would have defined “significantly under-inflated” as the tire pressure 20 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever was higher. It would have required the low tire pressure warning telltale to illuminate when any tire, or when each tire in any combination of tires, on the vehicle became significantly under-inflated.

The second alternative (three tires, 25 percent) would have defined “significantly under-inflated” as the tire pressure 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever was higher. The minimum levels of pressure were the same in both proposed alternatives. The alternative would have required the low tire pressure warning telltale to illuminate when any tire, or when each tire in any combination of tires, up to a total of three tires, became significantly under-inflated.

In most other respects, the two alternatives were identical. Both would have required passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less, manufactured on or after November 1, 2003, to be equipped with a TPMS and a low tire pressure warning telltale (yellow) to alert the driver. They would have required the telltale to illuminate within 10 minutes of driving after any tire on the vehicle became significantly under-inflated. They would have required the telltale to remain illuminated as long as any of the vehicle's tires remained significantly under-inflated, and the key locking system was in the “On” (“Run”) position. They would have required that the telltale be deactivatable, manually or automatically, only when the vehicle no longer had a tire that was significantly under-inflated. They would have required the TPMS in each vehicle to be compatible with all replacement or optional tires/rims of the size recommended for that vehicle by the vehicle manufacturer, i.e., each TPMS would have been required to continue to meet the requirements of the standard when the vehicle's original tires were replaced with tires of any optional or replacement size(s) recommended for the vehicle by the vehicle manufacturer. Finally, they would have required vehicle manufacturers to provide written instructions, in the owner's manual if one is provided, explaining the purpose of the low tire pressure warning telltale, the potential consequences of significantly under-inflated tires, and what actions drivers should take when the low tire pressure warning telltale is illuminated.

NHTSA believed that the only currently available TPMSs that would have been able to meet the requirements of the four-tire, 20 percent alternative were direct TPMSs. There were two reasons for this belief. First, currently available indirect TPMSs typically cannot detect significant under-inflation until the pressure in one of the vehicle's tires is about 30 percent below the pressure in at least some of the other tires. Second, they cannot detect when all four tires lose inflation pressure equally.

The agency believed that both currently available direct TPMSs and improved indirect TPMSs, but not current indirect TPMSs, would have been able to meet the requirements of the three-tire, 25 percent alternative.

In the NPRM, NHTSA anticipated that vehicle manufacturers would minimize their costs of complying with the three-tire, 25 percent alternative by installing improved indirect TPMSs in vehicles already equipped with ABSs and direct TPMSs in vehicles without ABSs. For vehicles already equipped with an ABS, the cost of modifying that system to serve the additional purpose of indirectly monitoring tire pressure would be significantly less than the cost of adding a direct TPMS. For vehicles not so equipped, adding a direct TPMS would be significantly less expensive than adding ABS to monitor tire pressure.

For the NPRM, NHTSA had two sets of data, one from Goodyear and another from NHTSA's Vehicle Research and Test Center (VRTC), on the effect of under-inflated tires on a vehicle's stopping distance. The Goodyear data indicated that a vehicle's stopping distance on wet surfaces is significantly reduced when its tires are properly inflated, as compared to when its tires are significantly under-inflated. The VRTC data indicated little or no effect on a vehicle's stopping distance. For purposes of the NPRM, NHTSA used the Goodyear data to establish an upper bound of benefits and the VRTC data to establish a lower bound. The benefit estimates below are the mid-points between those upper and lower bounds.

NHTSA estimated that the four-tire, 20 percent alternative would have prevented 10,635 injuries and 79 deaths at an average net cost of $23.08 per vehicle.

NHTSA estimated that the

three-tire, 25 percent alternative would have prevented 6,585 injuries and 49 deaths at an average net cost of $8.63 per vehicle.

NHTSA estimated that the net cost per equivalent life saved would have been $1.9 million for the four-tire, 20 percent alternative and $1.1 million for the three-tire, 25 percent alternative.

6 The range of injuries prevented was 0 to 21,270, and the range of deaths prevented was 0 to 158. These benefit estimates did not include deaths and injuries prevented due to reductions in crashes caused by blowouts and skidding/loss of control because the agency was unable to quantify those benefits at the time the NPRM was published. For this final rule, the agency was able to quantify those benefits. They are discussed in the Benefits section below. Net costs included $66.33 in vehicle costs minus $32.22 in fuel savings and $11.03 in tread wear savings. These cost estimates did not include maintenance costs. For this final rule, the agency has estimated maintenance costs. They are discussed in the Costs section below.

The range of injuries prevented was 0 to 13,170, and the range of deaths prevented was 0 to 97. Net costs included $30.54 in vehicle costs minus $16.40 in fuel savings and $5.51 in tread wear savings. These estimates did not include maintenance costs. The agency has estimated maintenance costs for this final rule.

Finally, the agency requested comments on whether a compliance phase-in with carry-forward credits would be appropriate. The agency suggested a phase-in period of 35 percent of production in the first year (2003), 65 percent in the second year, and 100 percent in the third year.

D. Summary of Public Comments on Notice

The agency received comments from tire, vehicle, and TPMS manufacturers, consumer advocacy groups, and the general public. In general, the tire manufacturers' comments, including the comments of the international tire industry associations European Tyre and Rim Technical Organisation (ETRTO), Japan Automobile Tyre Manufacturers Association (JATMA), and International Tire & Rubber Association (ITRA), echoed the comments of the Rubber Manufacturers Association (RMA). In general, the vehicle manufacturers' comments, including the comments of the Association of International Automobile Manufacturers (AIAM), were similar to the comments of the Alliance of Automobile Manufacturers (Alliance).

The tire manufacturers generally supported the four-tire, 20 percent alternative. The vehicle manufacturers generally supported requirements that would permit both direct and current indirect TPMSs to comply. TPMS manufacturers generally supported the alternative that would allow the type of system they manufacture. The consumer advocacy groups—Consumers Union and Advocates for Highway and Auto Safety (Advocates) supported by Public Citizen, Consumer Federation of America, and Trauma Foundation—generally supported the four-tire, 20 percent alternative. The general public was about evenly divided between those who supported and those who opposed a Federal standard requiring TPMSs.

The major issues discussed by the commenters are summarized below. The comments are addressed in the discussion of the final rule below

1. Vehicles Covered

The agency proposed to require TPMSs on passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less. The agency did not propose to require TPMSs on motorcycles, trailers, or low speed vehicles, or on medium (10,001-26,000 pounds GVWR) vehicles, or heavy (greater than 26,000 pounds GVWR) vehicles for reasons explained in the NPRM.

The Alliance recommended that the agency limit the applicability of the standard to these types of vehicles to those having a GVWR of 3,856 kilograms (8,500 pounds or less). The Alliance stated that the majority of vehicles above 8,500 pounds GVWR are used commercially. The Alliance argued that those vehicles are maintained on a regular basis and do not need a TPMS to assist in maintaining proper inflation pressure in the vehicles' tires.

The Alliance also recommended that the agency explicitly exclude incomplete vehicles, i.e., vehicles that are built in more than one stage, from the standard. Normally, the first-stage vehicle manufacturer is responsible for certifying that all vehicle systems that are not directly modified by subsequent-stage manufacturers meet all Federal motor vehicle safety standards. The Alliance stated that in the case of direct TPMSs, the first-stage manufacturer will be unable to guarantee that, even if physically undisturbed, a non-defective TPMS will function as designed after vehicle modifications (such as adding metal hardware to the vehicle or lengthening its wheelbase) are made by subsequent-stage manufacturers.

Advocates recommended that the agency expand the application of the standard to include medium (10,001-26,000 pounds GVWR) and heavy (over 26,000 pounds) trucks and buses. Advocates stated that tire under-inflation is a pervasive problem with these vehicles, especially given the high percentage of these vehicles that are equipped with re-treaded tires.

2. Phase-In Options and Long-Term Requirements

a. Definition of “Significantly Under-Inflated”

RMA recommended that the agency define “significantly under-inflated” as any inflation pressure that is less than the pressure required to carry the actual vehicle load on the tire per tire industry standards (or any pressure required to carry the maximum vehicle load on the tire if the actual load is unknown), or the minimum activation pressure specified in the standard, whichever is higher. RMA argued that some vehicles have a placard pressure that is barely adequate to carry the vehicle's maximum load. If the tire pressure falls 20 or 25 percent below the placard pressure, the tire pressure will be insufficient to carry the load. RMA stated that the definition of “significantly under-inflated” should not be tied to placard pressure unless the standard includes a requirement for all vehicles to have a reserve in the placard pressure above a specified minimum (e.g., 20 or 25 percent).

RMA also recommended that the agency change the minimum activation pressures for P-metric standard load tires from 20 to 22 psi and for P-metric extra load tires from 23 to 22 psi. Finally, RMA recommended that the agency change the “Maximum Pressure” heading in Table 1 to “Maximum or Rated Pressure” because light truck tires are not subject to maximum permissible inflation pressure labeling requirements. RMA recommended that the agency change the rated pressure for Load Range E tires from 87 to 80 psi. Finally, RMA, supported by the Retread/Repair Industry Government Advisory Council (RIGAC),

recommended that the agency adopt, in this rulemaking proceeding, an amendment to upgrade Standard No. 109, “New Pneumatic Tires,” by requiring that “a tire for a particular vehicle must have sufficient inflation and load reserve, such that an inflation pressure 20 or 25 percent less than the vehicle manufacturer's recommended inflation pressure is sufficient for the vehicle maximum load on the tire, as defined by FMVSS-110.”

RIGAC consists of representatives from the Tire Association of North America (TANA), Tread Rubber Manufacturers Group (TRMG), ITRA, and RMA.

Standard No. 110 specifies requirements for tire selection to prevent tire overloading.

The ITRA recommended that the agency consider only direct TPMSs. The ITRA stated that indirect TPMSs have too many limitations, including the inability to detect when all four of a vehicle's tires are significantly under-inflated. The ITRA claimed that, although direct TPMSs are more expensive than indirect TPMSs, their cost is minor when compared to their safety, handling, tread wear, and fuel economy benefits.

The Alliance recommended that the agency define “significantly under-inflated” as any inflation pressure 20 percent below a tire's load carrying

limit, as determined by a tire industry standardizing body (such as the Tire and Rim Association) or the minimum activation pressure specified in the standard, whichever is higher. The Alliance agreed with the agency's minimum activation pressure of 20 psi for P-metric standard load tires. The Alliance cited data from tests performed by RMA indicating that the average tire was able to operate at high speeds (120 and 140 km/h) at load-inflation conditions more extreme than the worst case that the Alliance proposal would allow.

The Alliance also stated that a 25 percent differential from placard pressure would be inadequate to allow the use of indirect TPMSs. The Alliance claimed that a minimum of 30 percent differential is necessary to ensure accuracy with an indirect TPMS and avoid excessive nuisance warnings.

The AIAM recommended that the agency define “significantly under-inflated” as any pressure more than 30 percent below the placard pressure. Alternatively, the AIAM suggested that the agency use the load-carrying limit of the tire as defined by a tire industry standardizing body as the baseline for determining the warning threshold.

Several manufacturers indicated that they are either developing or could develop indirect or hybrid TPMSs that perform better than current indirect TPMSs. In its comments on the NPRM, TRW Automotive Electronics (TRW), which manufactures both direct and indirect TPMSs, stated that it could, in concept, combine direct and indirect TPMS technologies to produce a hybrid TPMS that performs better than TRW's current indirect TPMS. TRW stated this could be accomplished by adding the equivalent of two direct pressure-monitoring sensors and a radio frequency receiver to an indirect TPMS. TRW suggested that this hybrid TPMS could comply detect 25 under-inflation for about 60 percent of the cost of a full direct TPMS. However, it did not indicate whether it had any plans to develop a hybrid system.

Sumitomo Rubber Industries, which manufactures indirect TPMSs, indicated that indirect TPMSs will be able to detect a 25 percent differential in inflation pressure.

Toyota, which uses an indirect TPMS on its Sienna van, stated that its next generation of indirect TPMSs (i.e., TPMSs not available for current production) would be able to detect a 20 percent differential in tire pressure by monitoring the resonance frequency as well as the dynamic radius changes of the tires. However, Toyota stated that this performance will be achieved only under ideal conditions, i.e., the vehicle is traveling in a relatively straight line at 30 to 60 km/h for at least 20 minutes. Thus, Toyota recommended that the agency adopt the Alliance proposal of 30 percent under-inflation. Toyota also stated that its next generation of indirect TPMSs would be able to detect significant under-inflation in all four tires. Toyota was not certain when its next generation of indirect TPMSs will be ready for implementation.

Advocates supported the definition of “significantly under-inflated” contained in the four-tire, 20 percent alternative, i.e., any pressure 20 percent or more below the placard pressure, or the minimum activation pressure specified in the standard. Advocates also supported the agency's minimum activation pressures.

b. Number of Tires Monitored

Advocates, the ITRA, and RMA recommended that the agency require TPMSs to be able to detect when all four of a vehicle's tires become significantly under-inflated. RMA argued that it is very likely that all four tires will lose air pressure at a similar rate and become significantly under-inflated within a six-month period.

RMA stated that drivers would rely heavily on TPMSs for tire pressure maintenance, which will make this scenario even more likely.

RMA stated that normal air pressure loss is approximately 1 to 2 psi per month.

The Alliance and AIAM recommended that the agency require only that TPMSs be able to detect significant under-inflation in a single tire. The Alliance argued that TPMSs are not meant to replace the normal tire maintenance that would detect pressure losses due to natural leakage and permeation. Instead, TPMSs are intended to detect a relatively slow leak due to a serviceable condition, such as a nail through the tread or a leaky valve stem. Since such leaks rarely affect more than one tire simultaneously, the Alliance argued, it is sufficient to require only that TPMSs be able to detect a single significantly under-inflated tire. In further support of this position, the Alliance argued that tires do not lose pressure at the same rate.

As noted above, TRW commented that a hybrid TPMS could be developed that would be capable of monitoring all four of a vehicle's tires. According to TRW, a hybrid system would involve installing two direct pressure sensors, one in a front wheel and one in a back wheel located diagonally from each other (

e.g.,

the front left and back right wheels), on a vehicle already equipped with an indirect TPMS. The pressure sensors would directly monitor the pressure in those two tires, while the indirect TPMS would use the wheel speed sensors to indirectly monitor the pressure in the other two tires. This would solve the problem indirect TPMSs have in detecting when two tires on the same axle or the same side of the vehicle become significantly under-inflated because a direct pressure sensor will be in a wheel on each axle and on each side of the vehicle. It would also solve the problem indirect TPMSs have in detecting when all four tires become significantly under-inflated.

Advocates and RMA also recommended that the agency require TPMSs to monitor a vehicle's spare tire. RMA argued that the spare tire should be monitored to ensure its functionality, if and when it is needed. Advocates stated, “Vehicle owners chronically neglect to maintain minimal air pressure in spare tires.”

The Alliance recommended that the agency require only that TPMSs monitor full-size, matching spare tires, and only when they are installed on the vehicle (i.e., not when they are stowed). The Alliance stated that temporary-use spare tires, including full-size, non-matching and compact spare tires, are not intended to be part of the normal tire rotation cycle for the vehicle. Because these temporary-use spare tires degrade the aesthetic appearance of a vehicle or have speed and distance limitations, vehicle owners normally replace them quickly. Thus, the Alliance recommended that the agency not require TPMSs to monitor temporary-use tires, whether stowed or installed on the vehicle.

RMA supported the agency's proposed requirement that TPMSs function properly with all replacement tires and rims of the size(s) recommended by the vehicle manufacturer. Advocates recommended that the agency require TPMSs to function properly with all replacement tires and rims, regardless of size.

The Alliance recommended that the agency require only that TPMSs function properly with those tires and rims offered as original or optional equipment by the vehicle manufacturer. The Alliance stated that there are a large number of replacement brands and types of tires and rims with different dynamic rolling radii, size variations, load variations, and temperature characteristics. The Alliance argued that since vehicle manufacturers do not control tire compliance for aftermarket tires and rims, they could not guarantee that the TPMS will work, or will work with the same level of precision, in all cases.

3. Lead Time

The Alliance and most vehicle manufacturers recommended the following four-year phase-in schedule: 15 percent of a manufacturer's affected products equipped with a semi- or fully-compliant TPMS in the first year; 35 percent in the second year; 70 percent in the third year; and 100 percent of a manufacturer's affected products equipped with a fully compliant TPMS in the final year. According to the Alliance, a semi-compliant TPMS is one that meets all but specified interface requirements, i.e., those concerning the display of information about under-inflation, and would be allowed only during the phase-in period. The Alliance and AIAM also recommended that the agency provide credits for early introduction of TPMSs to encourage early implementation of the standard.

TRW supported the agency's four-year phase-in period. TRW stated that direct TPMSs are ready so that manufacturers could start production to meet such a phase-in. However, TRW stated that the improvements in indirect TPMSs that will be necessary to meet the requirements of this final rule would make it difficult to meet the compliance date of November 1, 2003.

Ford Motor Company (Ford) commented that its recent experience with direct TPMSs demonstrates that this technology still needs a thorough prove-out. Ford stated that when it tested 138 direct pressure sensors on 30 vehicles, nine sensors experienced a malfunction. This translates to a sensor failure rate of 6.5 percent. However, Ford stated that if the final rule required five sensors per vehicle (all four tires plus the spare tire), nearly 33 percent of vehicles could experience the failure of at least one sensor. Ford recommended that the agency adopt the phase-in schedule set forth by the Alliance.

Vehicle Services Consulting, Inc. (VSC), which submitted comments on behalf of small volume vehicle manufacturers (i.e., those manufacturers who produce fewer than 5,000 vehicles worldwide each year), recommended that the agency provide phase-in discretion so that small volume manufacturers have until the end of the phase-in period before having to comply with the TPMS requirements. VSC claimed that small volume manufacturers could not obtain the TPMS technology at the same time as large volume manufacturers.

4. Reliability

In the NPRM, the agency noted that the components of direct TPMSs, especially when tires are taken off the rim, might be susceptible to damage. The agency requested comments on the likelihood of such damage. TRW stated:

Direct TPMSs are relatively new systems and, therefore, the likelihood of damage during driving or maintenance is unknown. However, direct TPMS sensors are designed to minimize the likelihood of damage during driving or maintenance operations. Most sensors are valve-mounted and rest in the drop center well of the rim, and are contoured to minimize the likelihood of damage during tire servicing. They can be packaged in a high impact plastic material, which can withstand high G forces and mechanical vibration/shock levels associated with the tire/wheel system. The likelihood of damage during operation is also minimized by the selected mounting location and the protection offered by the rim during flat conditions. These factors, combined with training for service center technicians, should reduce the overall likelihood of damage.

Beru Corporation, which manufacturers direct TPMSs, stated that it had sold over 800,000 direct TPMS wheel electronics and had received no reports of damage during operation or failures due to mounting error.

The European Community (EC) supported a rulemaking requiring TPMSs. The EC Stated, “The European Community is convinced (as is the NHTSA) of the appropriateness of a regulation in this field, and of its justification for the safety of road users.” The EC stressed “the paramount importance of reliability and accuracy of the technology.” The EC stated that “a temperature correction device might be a necessary feature in order to guarantee the reliability and accuracy of the device.”

5. Costs and Benefits Estimates

The Alliance stated that the benefits NHTSA estimated resulting from a reduction in stopping distance were based on three principal conclusions: (1) Properly inflated tires result in shorter stopping distances than under-inflated tires; (2) these shorter stopping distances have equal safety benefits in all types of crashes and under all environmental conditions; and (3) the benefits of shorter stopping distances associated with properly-inflated tires will be greater for direct TPMSs than for indirect TPMSs. The Alliance argued that each of these conclusions is highly questionable and not supported by the information in the rulemaking record.

The Alliance noted that in estimating the safety benefits resulting from stopping distance reductions, the agency relied on Goodyear data. The Alliance argued that these data “are neither conclusive with respect to the effect of under-inflation on stopping distance, nor reproducible according to the agency's own study demonstrating that there is no significant effect of tire under-inflation on stopping distance.” The Alliance also argued that even if the Goodyear data were valid, NHTSA's benefits estimates must be adjusted to claim benefits only for vehicles experiencing the same conditions as those in the Goodyear tests, i.e., all four of the vehicle's tires are at 17 psi or below and on wet pavement.

The Alliance questioned NHTSA's assumption that 80 percent of drivers would respond appropriately to a direct TPMS, but that only 60 percent of drivers would respond appropriately to an indirect TPMS. The Alliance argued that there was no evidence in the record supporting this assumption.

Goodyear conducted its tests on pavement with 0.05 inch water on the surface and found significant effects on stopping distance only when the pressure in the vehicle's tires was lowered to 17 psi.

Finally, the Alliance agreed that TPMSs should produce some of the unquantified benefits listed in the NPRM. However, the Alliance stated that there was no evidence that these benefits would be greater for direct TPMSs than for indirect TPMSs.

The ITRA stated that when developing training programs, it looks closely at tire performance and has the opportunity to analyze a significant number of tires that failed in service. They find that the single most common cause of tire failure is under-inflation. Thus, the ITRA claimed that the agency's benefits estimates may be under-stated.

TRW stated that current indirect TPMSs would have to be upgraded to meet the requirements of the three-tire, 25 percent alternative. TRW estimated that these upgrades would increase the cost of indirect TPMSs to 60 percent of the cost of a direct TPMS.

This estimate would apply only to vehicles that were already equipped with ABS.

IQ-mobil Electronics, a TPMS manufacturer in Germany, commented that it has developed “a batteryless transponder chip” that “costs half as much as the battery transmitter it replaces,” thus reducing “high replacement costs for the tire transmitter, and an annual environmental burden of millions of batteries.”

E. Submission of Draft Final Rule to OMB

Since this final rule is considered “significant” under Executive Order 12866, Regulatory Planning and Review, it was subject to review by the Office of Management and Budget (OMB) under that Order. The agency submitted a draft

final rule to OMB on December 18, 2001.

The draft final rule specified short and long-term performance requirements.

For the short term, it specified a phase-in of the TPMS requirements beginning November 1, 2003. During the phase-in, the draft final rule permitted vehicles to comply with either a four-tire, 25 percent option, which essentially would have required manufacturers to install direct TPMSs or improved indirect TPMSs, or a one-tire, 30 percent option, which would have permitted manufacturers to install either direct TPMSs or any type of indirect TPMSs, including current indirect TPMSs. For the long-term, the period beginning November 1, 2006, the requirements of the four-tire, 25 percent option would have become mandatory for all vehicles subject to the TPMS standard.

The rationales for the provisions of that draft final rule are discussed below in section VI.A., “Summary of Preliminary Determination about the Final Rule.”

As explained further below in section V.A. “Alternative Long-Term Requirements Analyzed in Making Preliminary Determination,” NHTSA analyzed three alternatives for the long term requirement in developing the draft final rule: a four-tire, 20 percent alternative, a three-tire, 25 percent alternative, and a four-tire, 25 percent alternative.

F. OMB Return Letter

After reviewing the draft final rule, OMB returned it to NHTSA for reconsideration, with a letter explaining its reasons for doing so, on February 12, 2002.

A copy of the return letter has been placed in the docket (Docket No. NHTSA-2000-8572-202). The letter also is available electronically at www.whitehouse.gov/omb/inforeg/dot_revised_tire_rtnltr.pdf.

In the letter, OMB stated its belief that the draft final rule and accompanying regulatory impact analysis did not adequately demonstrate that the agency had selected the best available method of improving overall vehicle safety. OMB said further that: NHTSA should base its decision about the final rule on overall vehicle safety, instead of just tire safety; while direct TPMSs can detect under-inflation under a greater variety of circumstances than indirect TPMSs, the indirect system captures a substantial portion of the benefit provided by direct systems; NHTSA should consider a fourth alternative for the long-term requirement, a one-tire, 30 percent compliance option, indefinitely, since it would allow vehicle manufacturers to install current indirect TPMSs; NHTSA, in analyzing long-term alternatives, should consider both their impact on the availability of ABS as well as the potential safety benefits of ABS; and that NHTSA should provide a better explanation of the technical foundation for the agency's safety benefits estimates and subject those estimates to sensitivity analyses.

G. Public Comments on OMB's Return Letter

Consumers Union (CU) and Public Citizen (PC) submitted comments on the OMB return letter.

Both letters have been placed in the docket. The CU letter is Docket No. NHTSA-2000-8572-204, and the PC letter is Docket No. NHTSA-2000-8572-199.

CU stated that direct TPMSs offer significant safety advantages over indirect TPMSs. CU recently performed tire air leakage testing and found that all four tires on a vehicle will likely lose pressure at a similar rate.

CU said that direct TPMSs could detect such pressure losses, while indirect TPMSs could not.

CU tested three samples of 36 tire models over a six-month period. CU mounted the tires on new rims and inflated the tires to 30 psi. Then CU stored the tires indoors at room temperature for six months and checked their inflation pressure each month. After six months, the average pressure loss was about 4.4 psi. A copy of CU's test procedures and the test results has been placed in the docket. (Docket No. NHTSA-2000-8572-203.)

CU questioned OMB's returning the TPMS final rule and asking NHTSA to consider the potential benefits of ABS in making a final decision on TPMS requirements. CU stated:

We cannot understand the logic of delaying an important safety measure like direct tire pressure monitoring systems while NHTSA studies issues related to a less effective alternative because that alternative might encourage automakers to make ABS more widely available.

Finally, CU stated that, while Congress mandated that NHTSA issue a regulation for TPMSs, Congress did not mandate that the agency issue a regulation requiring ABS to be installed in all vehicles.

PC also supported the four-tire, 20 percent alternative. PC argued that indirect TPMSs have shortcomings, including:

• They can detect under-inflation only if one tire is more than 25 percent less inflated than the other tires.

• They cannot detect when all four tires are equally under-inflated, a likely scenario if the tires are purchased or checked at the same time.

• They also cannot detect when two tires on the same side of the vehicle or the same axle are under-inflated, but can detect when diagonal tires are under-inflated.

PC also objected to OMB's returning the TPMS final rule and asking NHTSA to consider the potential benefits of ABS in making a final decision on TPMS requirements. PC questioned OMB's return letter, arguing that it employs

unproven assumptions about the cost and market effects of combining indirect systems with a requirement for anti-lock brakes (ABS) (a long-controversial area outside the focus of the agency's current rulemaking mandate), which, in turn, has only statistically insignificant and highly disputed safety effects.

PC also questioned the potential benefits of ABS cited by OMB. In response to OMB's reliance on a study by Charles Farmer, the PC asserted that Mr. Farmer

found that ABS

had no statistically significant effect on crash fatalities.

[Emphasis original.] Farmer was unable to determine whether ABS ultimately saved or cost lives across the vehicle fleet, making the “between 4 and 9 percent reduction” in crash fatalities [cited in the OMB letter] a statistical blip that may actually be zero percent.

H. Congressional Hearing

On February 28, 2002, the House Committee on Energy and Commerce held an oversight hearing on the implementation of the TREAD Act. During the hearing, several Congressmen discussed their expectations for the TPMS rulemaking. Expressing concern about the cumulative damage done to a tire that is run while under-inflated, Congressman Tom Sawyer asked whether a warning threshold of 25 percent below placard pressure was low enough. Given the potential for catastrophic failure of tires run too long while under-inflated, the Congressman stated that it was important that the TPMS not encourage drivers to drive on under-inflated tires.

Congressman Markey, the sponsor of the amendment that added the TPMS mandate to the TREAD Act, indicated that the reliance of drivers on the TPMS warning light could lead to safety problems if the TPMS does not provide sufficient warnings. He acknowledged that, during the consideration of the TPMS amendment, he had mentioned a TPMS that was then in use (an ABS-based TPMS on the Toyota Sienna). He said that while any TPMS was acceptable during the initial implementation period for the TPMS requirements, the real intent of the amendment is to provide a warning in all instances.

III. Safety Problem

Many vehicles have significantly under-inflated tires, primarily because drivers infrequently check their

vehicles' tire pressure. Other contributing factors are the difficulty of visually detecting when a tire is significantly under-inflated and the loss of tire pressure due to natural leakage and seasonal climatic changes.

A. Infrequent Driver Monitoring of Tire Pressure

Surveys have shown that most drivers check the inflation pressure in their vehicles' tires infrequently. For example, in September 2000, the Bureau of Transportation Statistics (BTS) conducted an omnibus survey for NHTSA. One of the questions posed was: “How often do you, or the person who checks your tires, check the air pressure in your tires?” The answers indicated that 29 percent of the respondents stated that they check the air pressure in their tires monthly; another 29 percent stated that they check the air pressure only when one or more of their vehicle's tires appears under-inflated; 19 percent stated that they only have the air pressure checked when the vehicle is serviced; 5 percent stated that they only check the air pressure before taking their vehicle on a long trip; and 17 percent stated that they check the air pressure on some other occasion. Thus, 71 percent of the respondents stated that they check the air pressure in the vehicles' tires less than once a month.

The agency notes that it seems likely that the respondents in both of the surveys cited overstated the frequency with which they check tire pressure, particularly given the fact that these surveys were conducted during the height of publicity about tire failures on sport utility vehicles in the late 2000 and early 2001.

In addition, NHTSA's National Center for Statistics and Analysis (NCSA) conducted a survey in February 2001. The survey was designed to assess the extent to which passenger vehicle drivers are aware of the recommended air pressure for their vehicles' tires, if drivers monitor air pressure, and to what extent actual tire pressure differs from placard pressure.

Data was collected through the infrastructure of the National Accident Sampling System—Crashworthiness Data System (NASS-CDS). The NASS-CDS consists of 24 Primary Sampling Units (PSUs) located across the country. Within each PSU, a random selection of zip codes was obtained from a list of eligible zip codes. Within each zip code, a random selection of two gas stations was obtained.

A total of 11,530 vehicles were inspected at these gas stations. This total comprised 6,442 passenger cars, 1,874 sports utility vehicles (SUVs), 1,376 vans, and 1,838 pick-up trucks. For analytical purposes, the data were divided into three categories: (1) Passenger cars; (2) pick-up trucks, SUVs, and vans with P-metric tires; and (3) pick-up trucks, SUVs, and vans with either light truck (LT) or flotation tires.

Drivers were asked how often they normally check their tires to determine if they are properly inflated. Their answers are in the following table:

How often is tire pressure checked?

Drivers of passenger cars (%)

Drivers of pick-up trucks, SUVs, and vans (%)

P-metric tires

LT or flotation tires

Weekly

8.76

8.69

8.16

Monthly

21.42

25.19

39.88

When they seem low

25.63

23.58

15.59

When serviced

30.18

27.72

25.54

For long trip

0.99

2.39

2.17

Other

6.46

8.27

6.97

Do not check

6.56

4.16

1.69

These data indicate that only about 30 percent of drivers of passenger cars, 34 percent of drivers of pick-up trucks, SUVs, and vans with P-metric tires, and 48 percent of drivers of pick-up trucks, SUVs, and vans with either LT or flotation tires claim that they check the air pressure in their vehicles' tires at least once a month.

B. Loss of Tire Pressure Due to Natural and Other Causes

According to data from the tire industry, 85 percent of all tire air pressure losses are the result of slow leaks that occur over a period of hours, days, or months. Only 15 percent are rapid air losses caused by contact with a road hazard, e.g., when a large nail that does not end up stuck in the tire punctures a tire.

Slow leaks may be caused by many factors. Tire manufacturers commented that tires typically lose air pressure through natural leakage and permeation at a rate of about 1 psi per month. Testing by CU supports those comments. In addition, tire manufacturers said that seasonal climatic changes result in air pressure losses on the order of 1 psi for every 10 degree F decrease in the ambient temperature. Slow leaks also may be caused by slight damage to a tire, such as a road hazard that punctures a small hole in the tire or a nail that sticks in the tire. NHTSA has no data indicating how often any of these causes results in a slow leak.

C. Percentage of Motor Vehicles With Under-Inflated Tires

During the February 2001 survey, NASS-CDS crash investigators measured tire pressure on each vehicle coming into the gas station and compared the measured pressures to the vehicle's placard pressure. They found that about 36 percent of passenger cars and about 40 percent of light trucks had at least one tire that was at least 20 percent below the placard pressure.

About 26 percent of passenger cars and 29 percent of light trucks had at least one tire that was at least 25 percent below the placard pressure. The agency notes those levels of under-inflation because they are the threshold levels for the low-tire pressure warning telltale illumination under the two alternatives the agency proposed in the NPRM for TPMSs. (66 FR 38982, July 26, 2001).

For purposes of this discussion, the agency classified pick-up trucks, SUVs, and vans with either P-metric, LT, or flotation tires as light trucks.

D. Consequences of Under-Inflation of Tires

1. Reduced Vehicle Safety—Tire Failures and Increases in Stopping Distance

When a tire is used while significantly under-inflated, its sidewalls flex more and the air temperature inside the tire increases, increasing stress and the risk of failure. In addition, a significantly under-inflated tire loses lateral traction,

making handling more difficult. Under-inflation also plays a role in crashes due to flat tires and blowouts. Finally, significantly under-inflated tires can increase a vehicle's stopping distance.

NHTSA's current crash files do not contain any direct evidence that points to low tire pressure as the cause of any particular crash.

However, this lack of data does not imply that low tire pressure does not cause or contribute to any crashes. The agency believes that it simply reflects the fact that measurements of tire pressure are not among the vehicle information included in the crash reports received by the agency and placed in its crash data bases.

In response to the TREAD Act, NHTSA has added new tire related variables and attributes, including tire make, model, recommended tire pressure, actual tire pressure, and tread depth to its crash databases. These new variables will provide more specific tire data for vehicles involved in crashes.

These crash databases are the NASS-CDS and the Fatality Analysis Reporting System (FARS).

The only tire-related data element in the agency's crash databases is “flat tire or blowout.” However, even in crashes for which a flat tire or blowout is reported, crash investigators cannot tell whether low tire pressure contributed to the tire failure.

The agency examined its crash files to gather information on tire-related problems that resulted in crashes. The NASS-CDS has trained investigators who collect data on a sample of tow-away crashes around the United States. These data can be weighted to generate national estimates.

The NASS-CDS General Vehicle Form contains a value indicating vehicle loss of control due to a blowout or flat tire. This value is used only when a vehicle's tire went flat, causing a loss of control of the vehicle and a crash. The value is not used for cases in which one or more of a vehicle's tires were under-inflated, preventing the vehicle from performing as well as it could have in an emergency situation.

NHTSA examined NASS-CDS data for 1995 through 1998 and estimated that 23,464 tow-away crashes, or 0.5 percent of all crashes, are caused by blowouts or flat tires each year. The agency placed the tow-away crashes from the NASS-CDS files into two categories: passenger car crashes and light truck crashes. Passenger cars were involved in 10,170 of the tow-away crashes caused by blowouts or flat tires, and light trucks were involved in the other 13,294.

NHTSA also examined data from the Fatality Analysis Reporting System (FARS) for evidence of tire problems in fatal crashes. In FARS, if tire problems are noted after the crash, the simple fact of their existence is all that is noted. No attempt is made to ascribe a role in the crash to those problems. Thus, the agency does not know whether the noted tire problem caused the crash, influenced the severity of the crash, or simply occurred during the crash. For example, a tire may have blown out and caused the crash, or it may have blown out during the crash when the vehicle struck some object, such as a curb.

Thus, while an indication of a tire problem in the FARS file gives some clue as to the potential magnitude of tire problems in fatal crashes, the FARS data cannot give a precise measure of the causal role played by those problems. The very existence of tire problems is sometimes difficult to detect and code accurately. Further, coding practices vary from State to State. Nevertheless, the agency notes that, from 1995 to 1998, 1.1 percent of all light vehicles involved in fatal crashes were coded as having tire problems. Over 535 fatal crashes involved vehicles coded with tire problems.

Under-inflated tires can contribute to types of crashes other than those resulting from blowouts or tire failure, including crashes which result from: skidding and/or a loss of control of the vehicle in a curve or in a lane change maneuver; an increase in a vehicle's stopping distance; or hydroplaning on a wet surface.

The 1977 Indiana Tri-level study associated low tire pressure with loss of control on both wet and dry pavements. The study never defined low tire pressure as a “definite” (i.e., 95 percent certainty that the crash would not have occurred absent this condition) cause of any crash, but did identify it as a “probable” (80 percent certainty that the crash would not have occurred absent this condition) cause of the crash in 1.4 percent of the 420 in-depth crash investigations.

The study divided “probable” cause into two levels: a “causal” factor and a “severity-increasing” factor. A “causal” factor was defined as a factor whose absence would have prevented the accident from occurring. A “severity-increasing” factor was defined as a factor whose presence was not sufficient, by itself, to result in the occurrence of the accident, but which resulted in an increase in speed of the initial impact. The study determined that under-inflated tires were a causal factor in 1.2 percent of the probable cause cases and a severity-increasing factor in 0.2 percent of the probable cause cases.

Note that more than one probable cause could be assigned to a crash. In fact, there were a total of 138.8 percent causes listed as probable causes (92.4 percent human factors, 33.8 percent environmental factors, and 12.6 percent vehicle factors). Thus, tire under-inflation's part of the total is one percent (1.4/138.8). The agency focused solely on the probable cause cases, which represent 0.86 percent of crashes (1.2/1.4 * 1.0).

Tires are designed to maximize their performance capabilities at a specific inflation pressure. When a tire is under-inflated, the shape of its footprint and the pressure it exerts on the road surface are both altered, especially on wet surfaces. An under-inflated tire has a larger footprint than a properly inflated tire. Although the larger footprint results in an increase in rolling resistance on dry road surfaces due to increased friction between the tire and the road surface, it also reduces the tire load per unit area. On dry road surfaces, the countervailing effects of a larger footprint and reduced load per unit of area nearly offset each other, with the result that the vehicle's stopping distance performance is only mildly affected by under-inflation.

On wet surfaces, however, under-inflation typically increases stopping distance for several reasons. First, as noted above, the larger tire footprint provides less tire load per area than a smaller footprint. Second, since the limits of adhesion are lower and achieved earlier on a wet surface than on a dry surface, a tire with a larger footprint, given the same load, is likely to slide earlier than the same tire with a smaller footprint because of the lower load per footprint area. The rolling resistance of an under-inflated tire on a wet surface is greater than the rolling resistance of the same tire properly-inflated on the same wet surface. This is because the slightly larger tire footprint on the under-inflated tire results in more rubber on the road and hence more friction to overcome. However, the rolling resistance of an under-inflated tire on a wet surface is less than the rolling resistance of the same under-inflated tire on a dry surface because of the reduced friction caused by the thin film of water between the tire and the road surface. The less tire load per area and lower limits of adhesion of an under-inflated tire on a wet surface are enough to overcome the increased friction caused by the larger footprint of the under-inflated tire. Hence, under-inflated tires cause longer stopping distance on wet surfaces than properly-inflated tires.

The agency has received data from Goodyear indicating that significantly under-inflated tires increase a vehicle's stopping distance.

The effects of tire under-inflation on vehicle stopping distance are discussed in greater detail in the agency's Final Economic Analysis (FEA).

Goodyear submitted these data to the docket in a letter dated September 14, 2001. See Docket No. NHTSA-2000-8572-160. OMB criticized NHTSA's application of these data to certain vehicle types in estimating safety benefits for this rulemaking. The agency responds to that criticism below in section VI.F., “Technical Foundation for NHTSA's Safety Benefit Analyses.” The Alliance also questioned NHTSA's use of the Goodyear data. The agency explains its use of the Goodyear data below in footnotes 22 and 23, and in the agency's Final Economic Analysis (FEA).

As explained in the FEA, the agency did not use the VRTC data or the Goodyear data that the agency used to estimate benefits in the NPRM because of concerns with the way in which the both tests were performed.

The agency believes that the more recent Goodyear test methodology adequately addressed these concerns.

For example, the VRTC only tested new tires, not worn tires that are more typical of the tires on most vehicles. In addition, the NHTSA track surface is considered to be aggressive in that it allows for maximum friction with tire surfaces. It is more representative of a new road surface than the worn surfaces experienced by the vast majority of road traffic. The previous Goodyear tests on wet surfaces were conducted on surfaces with .05 inch of standing water. This is more than would typically be encountered under normal wet road driving conditions. The agency expressed concerns with the adequacy of both sets of test data in a memo to the docket. (Docket No. NHTSA-2000-8572-81.)

For example, in its more recent tests Goodyear tested tires with two tread depths: full tread, which is representative of new tires, and half tread, which is representative of worn tires. Goodyear also conducted wet surface tests on surfaces with .02 inch of standing water, which is more representative of typical wet road driving conditions.

2. Reduced Tread Life

Unpublished data submitted to the agency by Goodyear indicate that when a tire is under-inflated, more pressure is placed on the shoulders of the tire, causing the tread to wear incorrectly.

The Goodyear data also indicate that the tread on an under-inflated tire wears more rapidly than it would if the tire were inflated to the proper pressure.

Docket No. NHTSA-2000-8572-26.

The Goodyear data indicate that the average tread life of a tire is 45,000 miles, and the average cost of a tire is $61 (in 2000 dollars). Goodyear also estimated that a tire's average tread life would drop to 68 percent of the expected tread life if tire pressure dropped from 35 psi to 17 psi and remained there. Goodyear assumed that this relationship was linear. Thus, for every 1-psi drop in tire pressure, tread life would decrease by 1.78 percent (32 percent/18 psi). This loss of tread life would take place over the lifetime of the tire. Thus, according to Goodyear's data, if the tire remained under-inflated by 1 psi over its lifetime, its tread life would decrease by about 800 miles (1.78 percent of 45,000 miles).

As noted above, data from the NCSA tire pressure survey indicate that 26 percent of passenger cars had at least one tire that was under-inflated by at least 25 percent. The average level of under-inflation of the four tires on passenger cars with at least one tire under-inflated by at least 25 percent was 6.8 psi. Thus, on average, these passenger cars could lose about 5,440 miles (6.8 psi under-inflation x 800 miles) of tread life due to under-inflation, if their tires were under-inflated to that extent throughout the life of the tires.

Also as noted above, data from the NCSA tire pressure survey indicate that about 29 percent of light trucks had at least one tire that was under-inflated by at least 25 percent. The average level of under-inflation of the four tires on light trucks with at least one tire under-inflated by at least 25 percent was 8.7 psi. Thus, on average, these light trucks could lose about 6,960 miles (8.7 psi under-inflation x 800 miles) of tread life due to under-inflation, if their tires were under-inflated to that extent throughout the life of the tires.

3. Reduced Fuel Economy

Under-inflation increases the rolling resistance of a vehicle's tires and, correspondingly, decreases the vehicle's fuel economy. According to a 1978 report, fuel efficiency is reduced by one percent for every 3.3 psi of under-inflation.

More recent data provided by Goodyear indicate that fuel efficiency is reduced by one percent for every 2.96 psi of under-inflation.

The Aerospace Corporation, Evaluation of Techniques for Reducing In-use Automotive Fuel Consumption, June 1978.

Docket No. NHTSA-2000-8572-26.

NHTSA notes that there is an apparent conflict between these data, which indicate that under-inflation increases rolling resistance and thus decreases fuel economy and the previously mentioned Goodyear data that indicates under-inflated tires increase a vehicle's stopping distance. While an under-inflated tire typically has a larger tread surface area (

i.e.,

tire footprint) in contact with the road, which might be thought to improve its traction during braking, the larger tire footprint also reduces the tire load per unit area. The larger footprint does result in an increase in rolling resistance on dry road surfaces due to increased friction between the tire and the road surface. On dry road surfaces, though, the countervailing effects of a larger footprint and reduced load per unit of area nearly offset each other, with the result that the vehicle's stopping distance performance is only mildly affected by under-inflation on those surfaces. However, as explained above in section III.D.1., “Reduced Vehicle Safety—Tire Failures and Increases in Stopping Distance,” on wet surfaces other attributes of under-inflation lead to increased stopping distances.

IV. Tire Pressure Monitoring Systems

There are currently two types of TPMSs: direct and indirect. Other types, including hybrid TPMSs that combine aspects of both direct and indirect systems, may be developed in the future. Direct TPMSs directly measure the pressure in a vehicle's tires, while indirect TPMSs estimate differences in pressure by comparing the rotational speed of the wheels. To varying degrees, both types can inform the driver when the pressure in one or more tires falls below a pre-determined level. Unless the TPMS is connected to an automatic inflation system, the driver must stop the vehicle and inflate the under-inflated tire(s), preferably to the pressure recommended by the vehicle manufacturer. Currently, TPMSs are available as original equipment on a few vehicle models. They are available also as after-market equipment, but few are sold. At this time, NHTSA does not have any information indicating that a hybrid TPMS is being planned for production. However, the agency received comments from TRW, a TPMS manufacturer, stating its belief that such a system could be produced.

The VRTC evaluated six direct and four indirect TPMSs that are currently available.

The VRTC found that the direct TPMSs were accurate to within an average of ±1.0 psi.

This leads the agency to believe that those current TPMSs are more accurate than the systems that were available at the time of the agency s 1981 rulemaking on TPMSs.

An Evaluation of Existing Tire Pressure Monitoring Systems, May 2001. A copy of this report is available in the docket. (Docket No. NHTSA-2000-8572-29.)

This is not to say that the systems were able to detect a 1.0 psi drop in pressure. The systems were accurate within ±1.0 psi once tire pressure had fallen by a certain percentage.

Following is a description of the two currently available types of TPMSs and their capabilities.

A. Indirect TPMSs

Current indirect TPMSs work with a vehicle's ABS. The ABS employs wheel speed sensors to measure the rotational speed of each of the four wheels. As a tire's pressure decreases, the rolling radius decreases, and the rotational speed of that wheel increases correspondingly. Most current indirect TPMSs compare the sums of the wheel speeds on each diagonal (i.e., the sum of the speeds of the right front and left rear wheels as compared to the sum of the speeds of the left front and right rear wheels). Dividing the difference of the sums by the average of the four wheels speeds allows the indirect TPMS to have a ratio that is independent of vehicle speed. This ratio is best expressed by the following equation: [(RF + LR) − (LF + RR)/Average Speed]. If this ratio deviates from a set tolerance, one or more tires must be over- or under-inflated. A telltale then indicates to the driver that a tire is under-inflated. However, the telltale cannot identify which tire is under-inflated. Current vehicles that have indirect TPMSs include the Toyota Sienna, Ford Windstar, and Oldsmobile Alero.

Current indirect TPMSs must compare the average of the speeds of the diagonal wheels for several reasons. First, current indirect TPMSs cannot compare the speed of one wheel to the speeds of the other three wheels individually or to the average speed of the four wheels. During any degree of turning, the outside tires must rotate faster than the inside tires. Thus, all four wheel speeds deviate significantly when the vehicle is in a curve or turn. If a current indirect TPMS compared each individual wheel speed to the average of all four wheels speeds, the system would provide a false alarm each time the vehicle rounded a curve or made a turn. The same would be true if the indirect TPMS compared each individual wheel speed to the speed of the other three wheels individually. Since the outside wheels would rotate much faster than the inside wheels in a curve or turn, each outside tire would appear to be under-inflated when compared to an inside tire.

Current indirect TPMSs also cannot compare the speeds of the front wheels to the speeds of the rear wheels because in curves, the front and rear wheels (on both sides of the vehicle) rotate at different speeds. This is primarily due to the fact that the front axle is steerable and follows a different trajectory than the rear axle. As a result, current indirect TPMS must compare a tire from each side and a tire from the front and rear axles to factor out the speed difference caused by curves and turns. Thus, current indirect TPMSs must compare the average speed of the diagonal wheels.

The VRTC tested four current ABS-based indirect TPMSs. None met all the requirements of either alternative proposed in the NPRM. All but one did not illuminate the low tire pressure warning telltale when the pressure in the vehicle's tires decreased to 20 or 25 percent below the placard pressure.

The VRTC determined that since reductions in tire diameter with reductions in pressure are very slight in the 15-40 psi range, most current indirect TPMSs require a 20 to 30 percent drop in pressure before they are able to detect under-inflation. The VRTC also concluded that those thresholds were highly dependent on tire and loading factors.

The Continental Teves indirect TPMS on the BMW M3 activated the warning telltale at pressures between 9 and 21 percent below the placard pressure.

The VRTC also found that none of the tested indirect TPMSs were able to detect significant under-inflation when all four of the vehicle's tires were equally under-inflated, or when two tires on the same axle or two tires on the same side of the vehicle were equally under-inflated. However, the VRTC did find that indirect TPMSs could detect when two tires located diagonally from each other (e.g., the front left and back right tires) became significantly under-inflated.

B. Direct TPMSs

Direct TPMSs use pressure sensors, located in each wheel, to directly measure the pressure in each tire. These sensors broadcast pressure data via a wireless radio frequency transmitter to a central receiver. The data are then analyzed and the results sent to a display mounted inside the vehicle. The type of display varies from a simple telltale, which is how most vehicles are currently equipped, to a display showing the pressure in each tire, sometimes including the spare tire. Thus, direct TPMSs can be linked to a display that tells the driver which tire is under-inflated. An example of a vehicle equipped with a direct system is the Chevrolet Corvette.

Since direct TPMSs actually measure the pressure in each tire, they are able to detect when any tire or when each tire in any combination of tires is under-inflated, including when all four of the vehicle's tires are equally under-inflated. Direct TPMSs also can detect small pressure losses. Some systems can detect a drop in pressure as small as 1 psi.

C. Hybrid TPMSs

In their comments on the NPRM, TRW, a manufacturer of both direct and indirect TPMSs, stated that in order to meet the proposed requirements of the 3-tire, 25 percent alternative, current indirect TPMSs would need the equivalent of the addition of two tire pressure sensors and a radio frequency receiver. The tire pressure sensors would be installed on wheels located diagonally from each other.

For the following reasons, the agency believes that such a “hybrid” TPMS would be able to overcome the limitations of current indirect TPMSs, i.e., the inability to detect when all four tires, or two tires on the same axle or same side of the vehicle are under-inflated. First, a hybrid TPMS would be able to detect when two tires on the same axle or the same side of the vehicle were under-inflated because one of those tires necessarily would contain a direct pressure sensor. Second, a hybrid TPMS would be able to detect when the two tires without a direct pressure sensor were under-inflated because they would be located diagonally from each other, and, as the VRTC found in its review of current TPMSs, current indirect TPMSs are able to detect when two tires located diagonally from each other are under-inflated. Third, a hybrid TPMS would be able to detect when three or four tires were under-inflated because one of those tires necessarily would contain a direct pressure sensor.

However, since the agency does not have any information indicating that a hybrid TPMS is currently being planned for production, the agency does not know when such a system could be produced.

V. Summary of Preliminary Determination About the Final Rule

In this section, NHTSA summarizes its preliminary determination about the final rule that was submitted to OMB in December 2001.

A. Alternative Long-Term Requirements Analyzed in Making Preliminary Determination

For purposes of the preliminary determination, the agency analyzed three alternatives. The first alternative (four tires, 20 percent) would have required a vehicle's TPMS to warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, fell to 20 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. The

second alternative (three tires, 25 percent) would have required a vehicle's TPMS to warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of three tires, fell to 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. The third alternative (four tires, 25 percent) combined aspects of the first two alternatives. It would have required a vehicle's TPMS to warn the driver when the pressure in any single tire or in each tire in any combination of tires, up to a total of four tires, fell to 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. The minimum levels of pressure specified in the standard would have been the same for all three alternatives.

The agency estimated that the four-tire, 20 percent alternative would have prevented from 141 to 145 fatalities and prevented or reduced in severity from 10,271 to 10,611 injuries per year.

The agency estimated that the average net cost of this alternative would have been from $76.77 to $77.53 per vehicle.

Since approximately 16 million vehicles are produced for sale in the United States each year, the total annual net cost of this alternative would have been from $1.228 billion to $1.241 billion. The net cost per equivalent life saved would have been from $5.1 million to $5.3 million.

NHTSA assumed that drivers would respond differently to different information displays. To get the upper bound, the agency assumed that manufacturers that installed direct TPMSs would also install a display showing the pressure of each tire. Currently only direct TPMSs are capable of displaying individual tire pressure. The agency also assumed that 33 percent of drivers would respond to such a display by re-inflating their tires when they became under-inflated by 10 percent, and that the other 67 percent would respond by re-inflating their tires when they became under-inflated by 20 percent, i.e., when the warning telltale would have been activated. To get the lower bound, the agency assumed that manufacturers would install only a low tire pressure warning telltale, as would have been required. Thus, all drivers would not re-inflate their tires until they became under-inflated by 20 percent, and the warning telltale was activated.

The net cost is the vehicle cost plus the maintenance cost minus the fuel and tread wear savings. The difference in costs is due to the cost of adding an individual tire pressure display. The agency assumed that manufacturers would install direct TPMSs on vehicles that are not equipped with ABS because the cost of adding a direct TPMS was significantly less than the cost of adding ABS and an indirect TPMS.

The agency estimated that the three-tire, 25 percent alternative would have prevented 110 fatalities and prevented or reduced in severity 7,526 injuries per year. The agency estimated that the average net cost would have been $63.64 per vehicle, and the total annual net cost would have been $1.018 billion. The net cost per equivalent life saved would have been $5.8 million.

The agency estimated that the four-tire, 25 percent alternative would have prevented 124 fatalities and prevented or reduced in severity 8,722 injuries per year. The agency estimated that the average net cost would have been $53.87 per vehicle, and the total annual net cost would have been $862 million. The net cost per equivalent life saved would have been $4.3 million.

The agency noted that the vehicle costs of these alternatives could be reduced in the future as manufacturers learned how to produce TPMSs more efficiently. Moreover, maintenance costs could be significantly reduced in the future if manufacturers could mass produce a direct TPMS that did not require the pressure sensors to be replaced when the batteries are depleted.

One TPMS manufacturer, IQ-mobil Electronics of Germany, indicated in its comments that it has developed a pressure sensor that does not require a battery.

NHTSA considered these three alternatives because the agency believed that TPMSs that complied with these alternatives would warn drivers of significantly under-inflated tires in a wide variety of reasonably foreseeable circumstances, including when more than one tire was significantly under-inflated. The agency also believed that improved indirect TPMSs could be developed to meet the requirements of the three-tire, 25 percent alternative and hybrid TPMSs could be developed to meet the three-tire, 25 percent and four-tire, 25 percent alternatives. Thus, the agency believed that these alternatives would provide an effective warning while striking a reasonable balance between encouraging further improvements in TPMS technology and stringency of the performance requirements and striking a reasonable balance between safety benefits and costs.

B. Phase-In and Long-Term Requirements

To facilitate compliance, the preliminary determination specified a four-year phase-in schedule,

During the phase-in, i.e., between November 1, 2003 and October 31, 2006, it would have allowed compliance with either of two options: a four-tire, 25 percent option or a one-tire, 30 percent option. Under the first option, a vehicle's TPMS would have had to warn the driver when the pressure in one or more of the vehicle's tires, up to a total of four tires, was 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. Under the second option, a vehicle's TPMS would have had to warn the driver when the pressure in any one of the vehicle's tires was 30 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure was higher. The minimum levels of pressure specified in the standard were the same for both compliance options.

Under both options, the preliminary determination would have required the low tire pressure warning telltale to remain illuminated as long as any one of the vehicle's tires remained significantly under-inflated, and the key locking system was in the “On” (“Run”) position. The telltale could have been deactivated automatically only when all of the vehicle's tires ceased to be significantly under-inflated, or manually in accordance with the vehicle manufacturer's instructions.

The preliminary determination would have required each TPMS to be compatible with all replacement or optional tires (but not rims) of the size(s) recommended for use on the vehicle by the vehicle manufacturer. It would also have required that the telltale perform a bulb-check at vehicle start-up. It specified written instructions explaining the purpose of the low tire pressure warning telltale, the potential consequences of significantly under-inflated tires, the meaning of the telltale when it was illuminated, and what actions drivers should take when the telltale is illuminated, to be placed in the vehicle's owner's manual.

The preliminary determination would not have required TPMSs to monitor the spare tire, either when the tire was stowed or when it was installed on the vehicle. It also would not have required the TPMS to indicate a system malfunction.

The agency created the one-tire, 30 percent option so that vehicle manufacturers could continue to install current indirect TPMSs for several more years, thus providing additional time and flexibility for innovation and technological development. The agency created the other option by adjusting the definition of “significantly under-inflated” for the four-tire option to 25 percent (instead of 20 percent) so that

improved indirect TPMSs and hybrid TPMSs could be used to comply with the TPMS standard. After the phase-in, i.e., after October 31, 2006, the second option would have been terminated, and the provisions of the first option would have become mandatory for all new vehicles.

The agency tentatively believed that a four-tire, 25 percent requirement was preferable for the long-term because it would require TPMSs that warn drivers about all combinations of significantly under-inflated tires and provide more timely and effective warnings. The agency tentatively believed that a one-tire, 30 percent requirement would allow TPMSs that do not warn about all combinations of significantly under-inflated tires and do not provide warnings until the extent of under-inflation reaches 30 percent below the placard pressure. Thus, it appeared that a four-tire, 25 percent requirement would better fulfill the purposes of the TPMS mandate in the TREAD Act, while encouraging further improvements in TPMS technology.

VI. Response to Issues Raised in OMB Return Letter About Preliminary Determination

Pursuant to section 6(a)(3) of Executive Order 12866, NHTSA is required to provide a written response to the points made by OMB in its February 12 return letter. As noted above, OMB stated in its return letter that: NHTSA should base its decision about the final rule on overall safety, instead of tire safety; while direct TPMSs can detect under-inflation under a greater variety of circumstances than indirect TPMSs, the indirect system captures a substantial portion of the benefit provided by direct systems; NHTSA should consider a fourth alternative for the long-term requirement, a one-tire, 30 percent compliance option, indefinitely, since it would allow vehicle manufacturers to install current indirect TPMSs; NHTSA, in analyzing long-term alternatives, should consider both their impact on the availability of ABS as well as the potential safety benefits of ABS; and that NHTSA should provide a better explanation of the technical foundation for the agency's safety benefits estimates and subject those estimates to sensitivity analyses.

A. Criteria for Selecting the Long-Term Requirement

1. Tire Safety and Overall Vehicle Safety

OMB stated in its return letter that “a rule permitting indirect systems may provide more overall safety than a rule that permits only direct or hybrid systems.” OMB said:

Although direct systems are capable of detecting low pressure under a greater variety of circumstances than indirect systems, the indirect system captures a substantial portion of the benefit provided by direct systems. Moreover, allowing indirect systems will reduce the incremental cost of equipping vehicles with anti-lock brakes, thereby accelerating the rate of adoption of ABS technology * * *. Both experimental evidence and recent real-world data have indicated a modest net safety benefit from anti-lock brakes.

While NHTSA's general obligation under the Vehicle Safety Act is to improve overall vehicle safety, it is mindful that its specific, immediate obligation in this rulemaking is to comply with the mandate of section 13 of the TREAD Act. The agency is seeking to comply with the mandate and safety goals of the TREAD Act in a way that encourages innovation and allows a range of technologies to the extent consistent with providing drivers with sufficient warning of low tire pressure under a broad variety of the reasonably foreseeable circumstances in which tires become under-inflated.

2. Statutory Mandate

Section 13 of the TREAD Act mandated the completion of “a rulemaking for a regulation to require a warning system in new motor vehicles to indicate to the operator when a tire is significantly under inflated” within one year of the TREAD Act's enactment. As noted below, the agency tentatively believes, based on the current record, that a four-tire, 25 percent under-inflation requirement would best meet the mandate.

B. Relative Ability of Direct and Current Indirect TPMSs To Detect Under-Inflation

As noted above, current indirect TPMSs work, in part, by adding the speeds of diagonal sets of tires and subtracting the sum of one set from the sum of the other. As a result, if all four tires are significantly under-inflated, and the difference in the tire pressures is not 30 percent or greater, current indirect TPMSs will not provide a warning. Similarly, if two tires on the same axle or same side of the vehicle are significantly under-inflated, current indirect TPMSs will not provide a warning.

These combinations of significantly under-inflated tires occur frequently enough that current indirect TPMSs would have provided a warning in only about 50 percent of the instances in which NHTSA found significant under-inflation in the February 2001 NCSA survey. Conversely, current direct TPMSs would have provided warnings in all those instances.

The following figures indicate how often current direct and indirect TPMSs would provide warnings when a vehicle has at least one tire that is at least 30 percent below the placard pressure.

Of the 5,967 passenger cars in the February 2001 NCSA survey, 1,199 (20 percent) had at least one tire that was at least 30 percent below the placard pressure. Current direct TPMSs would have provided a warning in every case, while current indirect TPMSs would have provided a warning in only 653 cases (54 percent).

Of the 3,950 light trucks in the NCSA survey, 789 (20 percent) had at least one tire that was at least 30 percent below the placard pressure. Current direct TPMSs would have provided a warning in every case, while current indirect TPMSs would have provided a warning in only 359 cases (46 percent).

Thus, of the total 9,917 passenger cars and light trucks in the NCSA survey, 1,988 (20 percent) had at least one tire that was at least 30 percent below the placard pressure. Current direct TPMSs would have provided a warning in every case, while current indirect TPMSs would have provided a warning in only 1,012 cases (51 percent).

Current indirect TPMSs would have failed to provide a warning in the remainder of the cases for various reasons. Many of the vehicles had one tire that was 30 percent below the placard pressure, but not 30 percent below the pressure in the other tires. As noted above, current indirect TPMSs require at least a 30 percent differential in tire pressure before providing a warning. Other vehicles had more than one tire that was 30 percent below the placard pressure. As noted above, current indirect TPMSs cannot detect when all four of a vehicle's tires, or two tires on the same side of the vehicle or the same axle, are under-inflated.

The absence of a warning in approximately 50 percent of the instances of significant under-inflation is a matter of concern given that many drivers will rely on a TPMS instead of regularly checking their tire pressure. Data from the July 2001 BTS omnibus survey indicate that 65 percent of people would be less concerned, to either a great extent or a very great extent, with routinely maintaining the pressure of their tires if their vehicle were equipped with a TPMS.

NHTSA notes that in its prepared statement submitted in connection with the February 28, 2002 hearing before the House Committee on Energy and Commerce on the TREAD Act, OMB stated: The 1-tire standard will provide warnings when 1 tire is underinflated but will not necessarily detect situations when 2 or more tires are underinflated. A further weakness of the 1-tire standard is that consumers may misperceive that their tires are fine (since the warning light is off) when in fact all four of their tires are equally underinflated. The 4-tire standard overcomes these problems.

C. Analysis of a Fourth Alternative Long-Term Requirement: One-Tire, 30 Percent Under-Inflation Detection

As explained above in section V.A., “Alternative Long-Term Requirements Analyzed in Making Preliminary Determination,” NHTSA analyzed three alternatives: a four-tire, 20 percent alternative; a three-tire, 25 percent alternative and a four-tire, 25 percent alternative.

OMB recommended that the agency analyze a fourth alternative that would require a vehicle's TPMS to warn the driver when the pressure in any one of the vehicle's tires is 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. (This alternative is referred to below as the “one-tire, 30 percent alternative.”) The agency's analysis of the benefits and costs of this alternative follows.

The agency estimates that the one-tire, 30 percent alternative would prevent 79 fatalities and prevent or reduce in severity 5,176 injuries. The agency estimates that the average per vehicle cost of this alternative would be $33.34. Since approximately 16 million light vehicles are produced for sale in the United States each year, the total annual cost of this alternative would be $533 million. The agency estimates that the average per vehicle maintenance cost would be $13.50,

and that the average per vehicle fuel and tread life savings over the lifetime of the vehicle would be $2.06 and $0.65, respectively. Thus, the net per vehicle cost of this alternative would be $44.13, and the total annual net cost would be $706 million. The net cost per equivalent life saved would be $5.8 million.

If the one-tire, 30 percent alternative were the only alternative available to vehicle manufacturers, the agency anticipates that the approximately

1/3

of vehicles not equipped with ABS would nevertheless comply by means of direct TPMSs. The approximately $40.91 of maintenance costs for each of those vehicles, if averaged over the entire fleet, is approximately $13.50.

D. Impact of One-Tire, 30 Percent Alternative on Installation Rate of ABS

OMB said that NHTSA should analyze the impact of adopting its long-term regulatory alternatives as well as an additional long-term alternative, a one-tire, 30 percent alternative, on the installation rate of ABS. Since the additional alternative is the only one that would permit compliance by means of installing current indirect TPMSs, and since OMB's suggestion that a TPMS standard could induce increased installation of ABS is dependent upon the manufacturers' being able to install that type of TPMS, NHTSA's analysis focuses on that alternative.

The agency believes there is no reliable basis for concluding that permitting current indirect TPMSs to comply would lead to a significant increase in installation of ABS in light vehicles for the following reasons.

First, the final rule does not mandate the installation of ABS. Vehicle manufacturers always have the option of providing a measure that exceeds NHTSA's standards. However, nothing in the final rule requires manufacturers to install ABS.

Second, the rulemaking record does not contain a reliable basis for concluding that manufacturers will voluntarily install ABS in significantly more light vehicles in response to being permitted to install current indirect TPMSs. When the Alliance addressed the issue of increased voluntary installation of ABS in its September 6, 2001 comments, it said only that a manufacturer “may well” opt to make ABS standard equipment on models for which optional ABS is currently available and is currently in high market demand. Further, only one manufacturer, Toyota, indicated that it might make ABS standard equipment on more vehicles if indirect TPMSs were allowed. Toyota provided this indication not in its written comments, but orally in a meeting with the agency. Nothing requires Toyota to make ABS standard equipment.

Third, several manufacturers orally indicated that they would not install ABS on their light trucks even if indirect TPMSs were allowed. General Motors (GM) and Ford told NHTSA that they would install a direct TPMS on their trucks, rather than a four-channel ABS and indirect TPMS, because ABS was significantly more expensive. Further, the agency notes that in April 2002, GM announced that it would cease offering ABS as standard equipment on a number of its less expensive models of cars to make those models more price competitive.

Fourth, it is not economically reasonable for manufacturers to install ABS voluntarily on significantly more vehicles in response to being permitted to install current indirect TPMSs. In the absence of written comments from individual manufacturers indicating that they are very likely to increase voluntarily their installation of ABS if allowed to install current indirect TPMSs, NHTSA may not simply assume that manufacturers will elect to spend $240 per vehicle to install ABS to save $53, the difference between the cost of a direct TPMS ($66) and an indirect TPMS ($13). The market for ABS has been static for several years, with the installation rate at about 63 percent. Absent a market demand for more installations, a manufacturer would not gain a market advantage by increasing the percentage of its vehicles with ABS.

In NHTSA's Final Economic Assessment (FEA), the agency states that although a manufacturer may elect to increase the installation of ABS, it is solely a marketing decision.

The influence, if any, this rulemaking might have on their marketing decisions is purely speculative. There are many factors that influence a manufacturer's decision to install equipment. Cost impact is only one of them.

A copy of the FEA has been placed in the docket.

E. Overall Safety Effects of ABS

In addition to recommending that the agency assume that the adoption of the one-tire, 30 percent compliance option would induce vehicle manufacturers to increase their installation of ABS, OMB also recommended that the agency take into account the potential safety benefits of ABS when estimating the benefits of that option. OMB suggested that ABS could reduce fatalities in light vehicles.

NHTSA has analyzed ABS and has determined that there is currently no statistically reliable basis for concluding that ABS reduces fatalities in light vehicles for the following reasons.

First, NHTSA has analyzed the impacts of ABS on light vehicle fatalities for the past decade, with mixed findings.

In general, test track results indicate that ABS is a very promising technology that enables drivers to keep vehicles under control under adverse road conditions. Under some pavement conditions, ABS allows the driver to stop a vehicle more rapidly while maintaining steering control, even during panic braking.

See “Preliminary Evaluation of the Effectiveness of Antilock Brake Systems for Passenger Cars,” NHTSA, December 1994, DOT HS 808 206. This study is available from the National Technical Information Service (NTIS) or NHTSA's Technical Reference Library.

However, the agency's analysis of real world crash data shows that, on balance, ABS has not been proven, thus far, to be greatly beneficial in real world fatal crashes.

NHTSA explored the desirability of requiring ABS on light vehicles in an

ANPRM issued in 1994 (59 FR 281; January 4, 1994) in response to the National Highway Traffic Safety Administration Authorization Act of 1991. (Public Law 102-240, December 18, 1991). The Act directed the agency to consider the need for any additional brake performance standards for passenger cars, including ABS standards. The ANPRM solicited comments about whether rulemaking was warranted to require that all light vehicles be equipped with ABS. It also posed a number of questions relative to the regulatory approaches that might be employed if requirements were imposed; the types of performance tests that might be used; varieties of ABSs that might be appropriate; and regulatory implementation strategies and schedules that might be employed if requirements were established.

Two years later, the agency issued a notice announcing that it had decided to defer indefinitely a decision whether to require equipping light vehicles with ABS. (61 FR 36698; July 12, 1996) In that notice, the agency stated that it was currently “inappropriate” to mandate ABS for the following reasons:

(1) Most studies that have analyzed the accident involvement experiences of ABS-equipped light vehicles have found mixed patterns, with a reduction in accidents in some crash modes but an increase in accidents in other crash modes, (2) even without a Federal requirement, a significant majority of light vehicles will be voluntarily equipped with ABS, (3) and requiring ABS on those light vehicles that will not be equipped with ABS would result in significant costs that, on balance, cannot be justified at this time.

In the 1996 notice, the agency lowered the prediction that it had made in its 1994 ANPRM that the rate of voluntary ABS installation in passenger cars would increase from 55 percent in 1994 to 85 percent in 1999. Given that there had been almost no increase in the rate between the 1994 model year and 1995 model year, the agency suggested in the 1996 notice that the rate in 1999 could be as low as 70 percent. Even that reduced figure has been shown by subsequent events to be overly optimistic. In 2000, the rate had reached only 63 percent for passenger cars.

The agency noted in the 1996 notice that the costs of bringing the percentages up to 100 percent for both passenger cars and light trucks could be very high, over $1.5 billion annually.

Since the 1996 notice, NHTSA has conducted additional studies. In one study, NHTSA measured the braking performance of a group of ABS-equipped production vehicles over a broad range of maneuvers on different road surfaces. Results of this study showed that for most maneuvers, ABS-assisted stops yielded shorter stopping distances in comparison to non-ABS vehicles.

“NHTSA Light Vehicle Antilock Brake System Research Program Task 4: A Test Track Study of Light Vehicle ABS Performance Over a Broad Range of Surfaces and Maneuvers,” January 1999, DOT HS 808 875, available at

http://www-nrd.nhtsa.dot.gov/vrtc/ca/capubs/NHTSAabsT4FinalRpt.pdf.

NHTSA has conducted several studies to examine possible reasons for the absence of overall safety benefits. One possible reason is that drivers are not adequately familiar or have inadequate or incorrect knowledge on the use of ABS. The agency has examined this possibility by conducting a national telephone survey to assess drivers' knowledge of ABS, its functionality and their expectations of its effects on vehicle performance. The results showed that, although most drivers had heard of ABS, many did not know what it did or how it affected vehicle performance.

“NHTSA Light Vehicle Antilock Brake System Research Program Task 2: National Telephone Survey of Driver Experiences and Expectations Regarding Conventional Brakes versus ABS,” November 2001, DOT HS 809 429, available at

http://www-nrd.nhtsa.dot.gov/vrtc/ca/capubs/abssurvey_rptfinal.pdf.

The agency also investigated whether the apparent increase in single vehicle crashes was due to driver “oversteering” in crash-imminent situations. The steering capability could have contributed to vehicles going off of the roadway during crash avoidance maneuvers. However, this steering activity was not found to result in a significant number of road departure crashes in NHTSA's research.

“Driver Crash Avoidance Behavior with ABS in an Intersection Incursion Scenario on Dry Versus Wet Pavement,” (SAE Paper No. 1999-01-1288), available at

http://www-nrd.nhtsa.dot.gov/vrtc/ca/lvabs.htm.

The agency also evaluated possible ABS-related behavioral adaptation of drivers through the collection of more detailed data about the driving behavior of subjects in a naturalistic research setting. This study did not indicate any statistically significant trend towards behavioral adaptation by drivers of ABS equipped vehicles in comparison to others.

“NHTSA Light Vehicle Antilock Brake System Research Program Task 7.1: Examination of ABS-Related Driver Behavioral Adaptation—License Plate Study,” November 2001, DOT HS 809 430, available at

http://www-nrd.nhtsa.dot.gov/vrtc/ca/capubs/abs71.pdf.

It is clear from the above comprehensive agency research efforts during the past five years that the agency still cannot explain why ABS systems do not produce the benefits anticipated from test track performance. Similarly, research by others has not yet succeeded in providing an explanation. Efforts by NHTSA and others continue today to try to explain this phenomenon.

Second, OMB's apparent conclusion that increased installation of ABS in light vehicles could have a modest net safety benefit is based upon data that are not statistically significant. Those data are taken from a study by Charles M. Farmer for the Insurance Institute for Highway Safety (IIHS).

“New Evidence Concerning Fatal Crashes by Passenger Vehicles Before and After Adding Antilock Braking System,” Charles M. Farmer, Insurance Institute for Highway Safety, February 2000. A copy of this study has been placed in the docket. (Docket No. NHTSA-2000-8572-206).

In the April 15, 2000 edition of its Status Report, IIHS said the following about the study:

New evidence suggests that cars with antilock braking systems no longer are disproportionately involved in certain types of fatal crashes. However, antilocks still aren't producing reductions in overall fatal crash risk * * *

* * * As before, vehicles with antilock brakes were less likely than cars with standard brakes to be in crashes fatal to occupants of other vehicles. At the same time, the vehicles with antilocks no longer were found to be overinvolved in crashes fatal to their own occupants. Particularly important is the reduction in single-vehicle, run-off-the-road crashes.

The data from the Farmer study are set forth in the table below:

All crashes

Fatalities in ABS cars

Fatalities in Non-ABS cars

95 Percent confidence bounds

Lower

Upper

1. GM cars in 1993-95

1.03

0.94

1.12

2. GM cars in 1996-98

0.96

0.87

1.05

3. GM cars in 1993-98

0.99

0.93

1.05

4. Non-GM cars in 1986-95

1.16 (Significant)

1.06

1.27

5. Non-GM cars in 1996-98

0.91

0.77

1.06

6. Non-GM cars in 1986-98

1.09 (Significant)

1.01

1.18

A ratio of 1.0 in the second column means that ABS did not have any effect on fatalities. A ratio above 1.0 indicates a higher risk of fatalities in ABS-equipped vehicles, while a ratio below 1.0 indicates a lower risk of fatalities in ABS equipped vehicles.

In order for the ratio for any group of vehicles to be statistically significant, both the lower and upper confidence bounds for that group must be either below 1.0 or above 1.0. This is true for only two groups of vehicles in the table: those in row 4, non-GM cars in 1986-95, and those in row 6, non-GM cars in 1986-98. For both of these groups, fatalities increased in ABS-equipped vehicles. Thus, in no subset of vehicles in the Farmer study is there any statistically significant advantage for ABS-equipped vehicles in crash fatalities.

OMB interpreted the study to indicate a 4-9 percent reduction in fatalities in ABS-equipped vehicles.

However, NHTSA does not believe that these data are statistically significant because one confidence bound is below 1.0 and the other is above 1.0. Thus, these alleged benefits are more than 5 percent likely to be due purely to chance.

The 4 percent figure is based on data for GM cars in 1996-98, while the 9 percent figure is based on data for non-GM cars in 1996-98.

Most statisticians consider data that are more than 5 percent likely to be due purely to chance to be statistically insignificant.

Mr. Farmer, the study's author, has indicated to NHTSA that people might have learned how to better use ABS by calendar years 1996-98, so that they were no longer at as great a risk of run-off-the-road fatal crashes as in prior years.

Even so, Farmer never stated in his study that ABS reduced fatalities. Regarding the Non-GM cars in 1996-98, he stated, “When all fatal crash involvements were considered, disregarding in which vehicle the fatalities occurred, the risk ratio was slightly lower than, but not significantly different from, 1.0.”

Mr. Farmer indicated this in an ex parte conversation with Jim Simons of NHTSA on February 14, 2002. (Docket No. NHTSA-2000-8572-210.)

Third, the most recent NHTSA study showed an improved picture regarding benefits and disbenefits compared to earlier studies, but still no overall benefits in fatal crashes.

The study examined ABS effects separately for passenger cars and light trucks for five types of crashes: frontal impacts, side impacts, rollover, run-off-the-road, and pedestrian.

“Analysis of the Crash Experience of Vehicles Equipped with All Wheel Antilock Braking Systems (ABS)—A Second Update Including Vehicles with Optional ABS,” NHTSA, DOT HS 809 144, September 2000. A copy of this study has been placed in the docket. (Docket No. NHTSA-2000-8572-205.) It is also available at

http://www-nrd.nhtsa.dot.gov/vrtc/ca/capubs/lvabstask1—crashdatareport.pdf.

The study found that, when both non-fatal and fatal crashes were combined, there were reductions in crashes for vehicles equipped with ABS. ABS was found to result in statistically significant reductions in crashes for most types of crashes, except side impact crashes, especially those involving cars.

However, when only fatal crashes were considered, there were not any statistically significant overall reductions of those crashes for ABS-equipped vehicles. In fact, the only statistically significant finding was that fatal light truck rollover crashes increased in vehicles with ABS as compared to vehicles without ABS. (That did represent an improvement over a 1998 study

that found statistically significant increases for several types of crashes.) No statistically significant effects, positive or negative, were found for any type of fatal passenger car crashes or for other types of fatal light truck crashes.

“An Analysis of the Crash Experience of Passenger Vehicles with Antilock Braking Systems-An Update,” NHTSA, DOT HS 808 758, August 1998.

It is unclear whether the evidence in recent studies represents a statistical aberration relative to earlier studies or whether it is indicative of a real and positive trend. NHTSA will continue to monitor the real world performance of ABS on light vehicles. As with all protective devices, NHTSA plans to update its estimates for ABS as more data become available. If NHTSA obtains data enabling it to show that ABS reduces net fatalities and is cost/beneficial in light vehicles, the agency will consider initiating a separate rulemaking to address the issue of whether to require their installation.

F. Technical Foundation for NHTSA's Safety Benefit Analyses

OMB recommended that NHTSA better explain the technical foundation for the agency's estimates of safety benefits and subject those estimates to sensitivity analyses.

Since conducting these desired sensitivity analyses is relevant primarily to making a decision about the TPMS requirements for the long-term, the agency believes that its decision to postpone the final decision on TPMS requirements to the second part of this final rule makes it unnecessary to conduct additional sensitivity analyses at this time.

When performing a sensitivity analysis, the agency changes assumptions it has made and then calculates differences in its benefits estimates. For example, the agency assumed that 20 percent of blowouts are caused by low tire pressure. If the agency performed a sensitivity analysis, it could change that assumption to 10 percent or 30 percent and then calculate a potential range of benefits.

The agency will complete its new study of TPMS by March 1, 2004. In this study, NHTSA will examine whether the tire pressure of vehicles without any TPMS are substantially closer to the vehicle manufacturer's recommended pressure than the tire pressure of vehicles with TPMSs, especially TPMSs that do not comply with the four-tire, 25 percent compliance option. If necessary, the agency will perform sensitivity analyses on these data.

OMB specifically questioned the estimates of safety benefits that NHTSA made based on reduced skidding and better control, since these estimates were based on the Indiana Tri-level study published in 1977. The agency does not have later data of this quality on the effects of under-inflation on crashes. The agency has started to collect tire pressure data as part of its NASS-CDS data collection. However, NASS-CDS is not a system designed to determine the cause of a crash. Thus, NHTSA does not anticipate receiving significant further data on this issue.

However, if this issue becomes a critical element for the decision for the second part of this final rule, the agency will

perform sensitivity analyses on the data from the 1977 study.

Although these data probably will not indicate whether low tire pressure caused a crash, the agency is collecting these data to determine the extent of the correlation between tire pressure and skidding/loss of control crashes.

OMB also noted NHTSA's use of Goodyear data, rather than VRTC data, on the effects of under-inflation on stopping distance. As explained in greater detail in the FEA, the agency did not use the VRTC data because of its concerns with the way in which the tests were performed.

The agency believes that the Goodyear test methodology adequately addressed these concerns.

For example, Goodyear tested tires with two tread depths: full tread, which is representative of new tires, and half tread, which is representative of worn tires.

In addition, OMB questioned the agency's use of the Goodyear data from a minivan to represent passenger cars. The critical element that is being measured is the difference in the tire's response when under-inflated. It is true that the absolute stopping distance will vary by vehicle weight and other vehicle performance characteristics. However, these same characteristics will influence both the properly inflated and the under-inflated tests in a similar fashion. Therefore, while Goodyear's test sample was confined to only two vehicles (a Dodge Caravan and a Ford Ranger), the differences measured under various inflation levels should still be indicative of the effect that could be expected.

Finally, OMB questioned NHTSA's assumption that under-inflation is involved in 20 percent of blowouts that cause crashes. The agency does not know precisely how many blowouts that cause crashes are influenced by under-inflation. As noted above in Section III.D.1., “Reduced Vehicle Safety—Tire Failures and Increases in Stopping Distance,” while the only tire-related data element in the agency's crash databases is “flat tire or blowout,” even in crashes for which a flat tire or blowout is reported, crash investigators cannot tell whether under-inflation contributed to the blowout. The agency's best estimate is that under-inflation plays a role in 20 percent of blowouts that cause crashes.

In making this estimate, the agency was mindful of the fact that many blowouts occur when one tire is punctured, begins to lose air at a rate somewhat faster than the normal rate due to natural causes, and then fails after being driven for some time while under-inflated. In these cases, a TPMS meeting either compliance option would be able to warn the driver of the under-inflated tire before the tire failed, possibly avoiding a crash.

NHTSA emphasizes that the choice of 20 percent as its estimate of the percentage of under-inflation's involvement in blowouts that cause crashes made little difference in the agency's benefits analyses. As noted below in Section VIII.A.3., “Flat Tires and Blowouts,” the agency estimates that the number of fatalities prevented per year due to reductions in crashes involving blowouts and flat tires will be 39 if all light vehicles meet the four-tire, 25 percent compliance option, and 32 if all light vehicles meet the one-tire, 30 percent compliance option. The choice of a somewhat higher or lower figure for the percentage of under-inflation's involvement would change only negligibly the relative benefits of the two compliance options.

VII. The Final Rule

A. Decision To Issue Two-Part Final Rule

As noted above, NHTSA was required to submit a draft final rule to OMB for review. The agency submitted a draft final rule to OMB on December 18, 2001. During the review process, OMB raised questions about the available data and the conclusions the agency preliminarily drew from them. OMB also raised questions about the effect of the final rule on the installation of ABS and the possibility of obtaining braking safety benefits as well as tire safety benefits.

To allow for the consideration of additional data regarding the requirements for vehicles manufactured after October 31, 2006, the agency has decided to divide the final rule into two parts. In this first part, the agency is establishing the requirements for vehicles manufactured from November 1, 2003 to October 31, 2006.

The agency will leave the rulemaking docket open for the submission of new data and analyses. During this period, the agency requests that commenters address how the performance characteristics of particular types of TPMSs satisfy the statutory requirement that systems provide a warning “when a tire is significantly under-inflated.”

NHTSA is especially interested in data and information about TPMS, both the systems in the field as well as systems under development. Commenters are urged to substantiate their comments with data and information to the maximum extent possible. Unsubstantiated comments are less useful.

The agency also will conduct a study comparing the tire pressures of vehicles without any TPMS to the pressures of vehicles with TPMSs, especially TPMSs that do not comply with the four-tire, 25 percent compliance option. Based on the record compiled to this date, the results of that study, and any other new information submitted to the agency, NHTSA will issue the second part of this rule. The second part will be issued by March 1, 2005, and will apply to vehicles that are manufactured after October 31, 2006.

Based on the record now before the agency, NHTSA tentatively believes that the four-tire, 25 percent option would best meet the mandate in the TREAD Act. However, it is possible that the new information may be sufficient to justify a continuation of the requirements in the first part of this rule, or some other alternative.

B. Part One of the Final Rule—November 2003 through October 2006

1. Summary

The first part of this final rule establishes requirements for vehicles manufactured between November 1, 2003, and October 31, 2006, subject to a phase-in schedule.

The final rule requires passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less, except those vehicles with dual wheels on an axle, to be equipped with a TPMS to alert the driver that one or more of the vehicle's tires are significantly under-inflated.

Under the phase-in, 10 percent of a manufacturer's affected vehicles will have to comply with one of the two compliance options the first year (vehicles manufactured between November 1, 2003 and October 31, 2004); 35 percent will have to comply the second year (between November 1, 2004 and October 31, 2005); and 65 percent will have to comply the third year (between November 1, 2005 and October 31, 2006).

For these vehicles, the first part of the final rule provides two compliance options.

Under the first compliance option, a vehicle's TPMS must warn the driver when the pressure in one or more of the vehicle's tires, up to a total of four tires, is 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. Under the second compliance option, a vehicle's TPMS must warn the driver when the pressure in any one of the vehicle's tires is 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure

for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher.

The agency is requiring manufacturers to irrevocably select the option to which they will certify each vehicle.

As noted above, the minimum levels of pressure are the same for both compliance options.

Vehicles certified to either compliance option will be required to provide written information in the owner's manual explaining the purpose of the low tire pressure warning telltale, the potential consequences of significantly under-inflated tires, the meaning of the telltale when it is illuminated, and what actions drivers should take when the telltale is illuminated. Vehicles certified to the one-tire, 30 percent option will be required to provide additional information on the inherent limitations of current indirect TPMSs.

Under both compliance options, the TPMS must include a low tire pressure-warning telltale (yellow). Under the four-tire, 25 percent option, the telltale must remain illuminated as long as any of the vehicle's tires remains significantly under-inflated, and the key locking system is in the “On” (“Run”) position. The telltale can be deactivated automatically only when all of the vehicle's tires cease to be significantly under-inflated, or manually in accordance with the vehicle manufacturer's instructions.

The one-tire, 30 percent option requires that the telltale remain illuminated as long as one of the vehicle's tires remains significantly under-inflated, and the key locking system is in the “On” (“Run”) position. The telltale can be deactivated automatically only when that tire ceases to be significantly under-inflated, or manually in accordance with the vehicle manufacturer's instructions.

Since indirect TPMSs do not actually monitor tire pressure, they must be told when the vehicle's tires have been re-inflated. Thus, indirect TPMSs require the driver to push a reset button after re-inflating the vehicle's tires.

Both compliance options require that the low tire pressure-warning telltale perform a bulb-check at vehicle start-up.

Under both compliance options, each TPMS must be compatible with all replacement or optional tires (but not rims) of the size(s) recommended for use on the vehicle by the vehicle manufacturer. The TPMS is not required to monitor the spare tire, either when it is stowed or when it is installed on the vehicle. The TPMS also does not have to indicate a system malfunction.

In response to comments regarding the need to manually reset indirect TPMSs after adding pressure to the tires, the agency is permitting the warning telltale to be deactivated manually, in accordance with the vehicle manufacturer's instructions.

In response to comments regarding variations in rim designs, the agency is requiring TPMSs to be compatible with all replacement or optional tires, but not rims, of the size(s) recommended for use on the vehicle by the vehicle manufacturer.

In response to BTS survey data indicating that 65 percent of people would be less concerned to either a great extent or a very great extent with routinely maintaining their tire pressure if their vehicle were equipped with a TPMS, the agency is requiring the low tire pressure warning telltale to perform a bulb-check during vehicle start-up.

In response to comments, the agency is also making minor changes to the required written instructions, and requiring vehicles certified to the one-tire, 30 percent option to provide additional information on the inherent limitations of current indirect TPMSs.

2. Congressional Intent

Section 13 of the TREAD Act simply mandates “a rulemaking for a regulation to require a warning system in new motor vehicles to indicate to the operator when a tire is significantly under inflated.” None of the sources of legislative history commonly recognized as being legally authoritative, such as the House and Senate Reports or the Congressional Record, shed any light on the type of TPMS that Congress intended to mandate with this amendment.

The agency also notes that the issue of direct vs. indirect TPMSs was not before Congress when the bill that became the TREAD Act was being considered.

In the absence of any legally authoritative sources, the Alliance turned in its comments to statements made by Congressman Markey, the sponsor of the TPMS amendment, as quoted in an unofficial transcript of the House Committee on Energy and Commerce markup of the bill that became the TREAD Act.

In explaining and arguing for his amendment, Congressman Markey referred to a TPMS on an existing vehicle model. That TPMS was an indirect TPMS. Based on the Congressman's having mentioned an indirect TPMS in the course of his remarks, the Alliance argued that the Congressman must have intended that current indirect TPMSs be allowed under the rulemaking mandated by the TPMS amendment.

This sort of legislative history is not entitled to much, if any, weight.

While the Alliance's interpretation of Congressman Markey's statements during markup is not inconsistent with those statements, it goes well beyond anything that the Congressman directly said in them. Further, that interpretation is contrary to Congressman Markey's statements at the February 28, 2002 House Committee on Energy and Commerce hearing. In those later statements, Congressman Markey said that the intent of his TPMS amendment was to require TPMSs that provide warnings in all instances of under-inflation, thus suggesting a preference for direct TPMSs, which can provide such warnings, over current indirect TPMSs, which cannot. While those statements at the hearing likewise do not constitute any legally authoritative legislative history of the TREAD Act, they do suggest that the Alliance's interpretation of Congressman Markey's earlier statements is not persuasive.

3. Vehicles Covered

The final rule requires TPMSs on passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less, except those vehicles with dual wheels on an axle. It does not require TPMSs on motorcycles, trailers, low-speed vehicles, medium vehicles, or heavy vehicles.

NHTSA is not requiring TPMSs on motorcycles because, unlike the types of vehicles that are subject to the final rule, some motorcycles still use tubed tires. In order for a direct TPMS to work with tubed tires, the pressure sensor would not only have to be inside the tire, but also inside the tube itself. The agency is not aware of any TPMSs that are made to work with tubed tires. The agency requested comments on this issue but received none.

Advocates recommended that the agency open rulemaking to set regulatory requirements for retreaded and recapped medium (10,001—26,000 pounds GVWR) and heavy (over 26,000 pounds) vehicle tires. Advocates stated that there is a “serious, pervasive problem of tire underinflation among medium and heavy vehicles, especially given the high percentage of trucks and buses above 10,000 pounds gross vehicle weight which use re-treaded tires.” However, Advocates did not provide any data to support this statement.

As discussed in the NPRM, NHTSA is not requiring TPMSs on medium (10,001—26,000 lbs. GVWR) and heavy (greater than 26,001 lbs. GVWR) vehicles at this time for two reasons. First, this rulemaking is required by the TREAD Act, which required a final rule to be issued in one year and was passed in response to problems with certain Firestone tires. Since those tires were

used on light vehicles, and the time frame was so tight, the agency has limited its study of under-inflation to light vehicles.

Second, the issues associated with under-inflated tires on medium and heavy vehicles are different from and more complex than the issues associated with under-inflated tires on light vehicles. For example, medium and heavy vehicles are equipped with tires that are much larger and have much higher pressure levels than the tires used on light vehicles. In addition, medium and heavy vehicles are generally equipped with more axles and tires than light vehicles. Since the TREAD Act imposed a one-year deadline on this rulemaking, the agency did not have the time to study and analyze those issues sufficiently.

The Alliance recommended that the agency limit the applicability of the standard to vehicles having a GVWR of 3,856 kilograms (8,500 pounds or less). The Alliance stated that the majority of vehicles above 8,500 pounds GVWR are used commercially. The Alliance argued that such vehicles are maintained on a regular basis and do not need a TPMS to assist in maintaining proper inflation pressure in the vehicles' tires.

NHTSA is aware of at least two non-commercial vehicle models—the Chevrolet Suburban and Ford Excursion, both SUVs—that have a GVWR between 8,500 and 10,000 pounds. In addition, 15-passenger vans are typically in this weight rating range. If the agency adopted the Alliance's recommendation, these vehicles would be excluded from the standard. These vehicles are as subject to under-inflated tires as other light SUVs and vans. Thus, the agency is not adopting the Alliance's suggestion.

However, to address the Alliance's concern about the standard's applicability to commercial vehicles, the agency is excluding from the standard trucks, buses, and multipurpose passenger vehicles that have a GVWR under 10,000 pounds and dual wheels on an axle. This includes vehicles such as step vans, tow trucks, and some large pick-up trucks. The agency notes that these vehicles are normally used in a commercial capacity, and, as the Alliance argued, commercial vehicles normally undergo maintenance on a regular basis. Thus, these vehicles are less likely to experience significantly under-inflated tires. Moreover, since these vehicles have more wheels on an axle, they are less likely to experience the adverse effects on vehicle handling and other safety problems associated with significantly under-inflated tires.

The Alliance also recommended that the agency explicitly exclude incomplete vehicles from the standard.

Normally, the first-stage vehicle manufacturer is responsible for certifying that all vehicle systems that are not directly modified by subsequent-stage manufacturers meet all Federal motor vehicle safety standards. The Alliance stated that, in the case of direct TPMSs, the first-stage manufacturer will be unable to guarantee that, even if physically undisturbed, a non-defective TPMS will function as required after vehicle modifications (such as adding metal hardware to the vehicle or lengthening its wheelbase) are made by subsequent-stage manufacturers.

49 CFR Part 568.3 defines “incomplete vehicle” as “an assemblage consisting, as a minimum, of frame and chassis structure, power train, steering system, suspension system, and braking system, to the extent that those systems are to be part of the completed vehicle, that requires further manufacturing operations, other than the addition of readily attachable components, such as mirrors or tire and rim assemblies, or minor finishing operations such as painting, to become a completed vehicle.”

The agency notes that many incomplete vehicles are manufactured into custom vans and recreational vehicles. The agency believes that these vehicles should be equipped with the same or similar safety systems as passenger cars, multipurpose passenger vehicles, trucks, and buses. In particular, the agency believes that these types of vehicles should be equipped with a TPMS, as they are just as likely to experience significantly under-inflated tires as other light vehicles. In addition, the agency notes that if subsequent-stage manufacturers modify the TPMS on a vehicle, they will be responsible for certifying that the vehicle meets the standard. Therefore, the agency is not adopting the Alliance's suggested exclusion of incomplete vehicles.

4. Phase-In Options and Requirements

a. Alternatives Considered

For purposes of this first part of the final rule, the agency considered four alternatives, three of which are discussed above in section V.A., “Alternative Long-Term Requirements Analyzed in Making Preliminary Determination.” The fourth alternative considered by the agency is the one-tire, 30 percent alternative suggested by OMB. This alternative would require a vehicle's TPMS to warn the driver when the pressure in any one of the vehicle's tires is 30 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure is higher. The benefits and costs of the one-tire, 30 percent alternative are discussed above in section VI.C. “Analysis of a Fourth Alternative Long-Term Requirement: One-Tire, 30 Percent Under-Inflation Detection.”

While the agency ultimately considered four alternatives, in the NPRM the agency proposed only two alternative versions of a standard for TPMSs and requested comments on them. The two alternatives were the four-tire, 20 percent alternative and the three-tire, 25 percent alternative.

To simplify the agency's analysis and discussion of the comments, NHTSA is separately addressing below the two most significant aspects of these two alternatives,

i.e.,

the definition of the term “significantly under-inflated” and the number of tires the TPMS should monitor.

In the NPRM, the agency provided two alternate definitions of the term “significantly under-inflated,” and then used that term in specifying performance requirements for the low tire pressure warning telltale, while not specifying any performance requirements for the TPMS itself. After reviewing this approach to drafting and organizing the regulatory text, the agency decided to adopt a simpler, more direct approach. Instead of defining the term “significantly under-inflated” in the final rule, the agency is specifying performance requirements, including the threshold level of under-inflation that must trigger a warning, for two compliance options: the four-tire, 25 percent option and the one-tire, 30 percent option.

i. Threshold Level of Under-Inflation

As explained above in section II.D, “Summary of Public Comments on Notice,” RMA recommended that the agency define “significantly under-inflated” as any inflation pressure that is less than the pressure needed to carry the actual vehicle load on the tire per tire industry standards (or any pressure required to carry the maximum vehicle load on the tire if the actual load is unknown), or the minimum activation pressure specified in the standard, whichever is higher. RMA also recommended that the agency change the minimum activation pressures for P-metric standard load tires from 20 to 22 psi and for P-metric extra load tires from 23 to 22 psi. RMA also recommended that the agency change the “Maximum Pressure” heading in Table 1 to “Maximum or Rated Pressure” because light truck tires are not subject to maximum permissible inflation pressure labeling requirements. RMA recommended that the agency change

the rated pressure for Load Range E tires from 87 to 80 psi. Finally, RMA, supported by RIGAC, recommended that the agency adopt a requirement in the agency's separate rulemaking to upgrade Standard No. 109, “New Pneumatic Tires,” that “a tire for a particular vehicle must have sufficient inflation and load reserve, such that an inflation pressure 20 or 25 percent less than the vehicle manufacturer's recommended inflation pressure is sufficient for the vehicle maximum load on the tire, as defined by FMVSS-110.”

Standard No. 110 specifies requirements for tire selection to prevent tire overloading.

The ITRA recommended that the agency consider only direct TPMSs. The ITRA stated that indirect TPMSs have too many limitations, including the inability to detect when all four of a vehicle's tires are significantly under-inflated. The ITRA claimed that although direct TPMSs are more expensive than indirect TPMSs, their benefits outweigh their costs.

The Alliance recommended that the agency define “significantly under-inflated” as any inflation pressure 20 percent below a tire's load carrying limit, as determined by a tire industry standardizing body (such as the Tire and Rim Association) or the minimum activation pressure specified in the standard, whichever is higher. The Alliance agreed with the agency's minimum activation pressure of 20 psi for P-metric standard load tires.

The AIAM recommended that the agency define “significantly under-inflated” as any pressure more than 30 percent below the placard pressure. Alternatively, the AIAM suggested that the agency use the load carrying limit of the tire as defined by a tire industry standardizing body as the baseline for determining the warning threshold.

TRW stated that indirect TPMSs that are currently on the market could be improved to detect a 25 percent differential in inflation pressure. TRW stated this could be accomplished by adding the equivalent of two direct pressure sensors and a receiver to an indirect TPMS.

Advocates supported the definition of “significantly under-inflated” contained in the first alternative,

i.e.,

any pressure 20 percent or more below the placard pressure, or the minimum activation pressure specified in the standard, whichever is higher.

The agency notes that both RMA and the Alliance recommend that the agency tie the definition of “significantly under-inflated” to the load carrying capacity of the tire rather than the placard pressure. NHTSA declines to adopt this recommendation for two reasons.

First, the placard pressure provided by the vehicle manufacturer assumes loading at GVWR and also takes into consideration ride, handling, and other factors for safe vehicle operation. Some manufacturers also include a certain amount of reserve load capacity in the event that the tire is overloaded. Therefore, when tire pressure is down to 25 percent below the placard pressure, it is not necessarily below the pressure that is needed to safely carry the weight of the vehicle. Moreover, the agency notes that the calculations in the Tire and Rim Association (T&RA) tables are based on the volume of air in the tire, and do not consider differing performance capabilities of different tire materials or manufacturing quality.

These tables, contained in the T&RA yearbook, establish the load carrying capacity of a tire at a specific inflation pressure.

Second, consumers are currently not familiar with using the T&RA tables to determine the correct tire inflation pressure for their vehicles. However, they do have some familiarity with using the vehicle's placard pressure to maintain proper inflation pressures. It would be counter-productive to introduce a new frame of reference for consumers to use at this time unless there are compelling reasons to do so.

The agency agrees with the Alliance's statement that most current indirect TPMSs are not able to detect a 25 percent differential from placard pressure. Of the indirect TPMSs evaluated by the VRTC, only one was capable of activating the warning telltale at pressures at least 25 percent below the placard pressure.

The indirect TPMS is manufactured by Continental Teves for the BMW M3. In the testing, it was able to detect when one, two (only if diagonally opposite each other) or three tires were significantly under-inflated.

The agency believes that, as the technology matures, manufacturers will be able to improve the performance of indirect TPMSs. TRW, which manufactures both direct and indirect TPMSs, stated that the indirect TPMSs currently on the market could be improved to detect a 25 percent differential from placard pressure. However, TRW was not certain that these improvements could be developed and implemented by the 2003 effective date of the final rule. Sumitomo's comments indicated that indirect TPMSs would be able to detect a 25 percent differential in inflation pressure. Toyota stated that its next generation of indirect TPMSs would be able to detect a 20 percent differential in tire pressure by monitoring the resonance frequency as well as the dynamic radius changes of the tires.

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