Heavy-Duty Vehicles, Air Pollution, and Climate Change

Updated February 14, 2023

Heavy-Duty Vehicles, Air Pollution, and Climate Change

In August 2021, the Biden Administration announced plans

to reduce greenhouse gas (GHG) emissions and other air

pollutants from medium- and heavy-duty vehicles and

engines through a series of rulemakings over three years

(Executive Order 14037 of August 5, 2021, “Strengthening

American Leadership in Clean Cars and Trucks,” 86

Federal Register 43583). The first rule, promulgated by the

U.S. Environmental Protection Agency (EPA) in January

2023, set new standards for nitrogen oxides (NOx) and other

criteria pollutant emissions for new medium- and heavyduty vehicles and engines starting in model year (MY)

2027. A second rule, to be promulgated by EPA and the

National Highway Traffic Safety Administration (NHTSA),

is expected to set more stringent GHG emission and fuel

efficiency standards for the sector beginning with MY2027.

Emissions from Heavy-Duty Vehicles

The medium- and heavy-duty vehicle and engine sector

(defined at 40 C.F.R. §1037 and 49 C.F.R. §523) generally

includes tractor-trailers, vocational vehicles, buses, and

heavy-duty pickup trucks and vans. EPA reports that

“pollution from heavy-duty trucks contributes to poor air

quality and health across the country, especially in

overburdened and underserved communities.” These

vehicles are the largest contributor to mobile source

emissions of NOx (about 32% in 2017, the most recently

available inventory; NOx reacts in the atmosphere to form

ground-level ozone, or smog), as well as particulate matter,

carbon monoxide, and air toxics. Further, according to

EPA’s Inventory of U.S. Greenhouse Gas Emissions and

Sinks: 1990–2019 (published April 2021), medium- and

heavy-duty vehicles emitted 456.6 million metric tons of

carbon dioxide (CO2) in 2019 (about 25% of total CO2

emissions from the U.S. transportation sector).

Current Standards

Criteria Pollutant Emission Standards

In January 2023, EPA finalized the current set of emission

standards for criteria, or common, pollutants from heavyduty vehicles and engines (88 Federal Register 4269)

through its authorities under the Clean Air Act (CAA). The

new standards, to begin in MY2027, would require original

equipment manufacturers to reduce tailpipe emissions of

NOx by approximately 80% and particulate matter by 50%,

compared with the previous standards, and increase the

regulatory useful life period of vehicles by 1.5-2.5 times

and the emissions warranty period by 2.8-4.5 times,

depending on the class of vehicle. The rule requires

manufacturers to better ensure engines and emission control

systems work properly on the road for a longer period of

time and to demonstrate that engines are designed to

prevent vehicle drivers from tampering with emission

control devices. EPA estimated that by 2045, the rule would

result in, inter alia, up to 2,900 fewer premature deaths;

18,000 fewer cases of childhood asthma; and $29 billion in

annual net benefits. EPA also estimated the technology

required to meet the new rule will cost between $2,500 and

$8,300 per vehicle.

On February 9, 2023, S.J.Res. 11 was introduced in

Congress, providing for disapproval of EPA’s January 2023

heavy-duty vehicles rule under the Congressional Review

Act. Sponsors of the resolution state that the new standards

are overly challenging to implement, would make the cost

of new trucks prohibitive for small business owners

(potentially increasing pollution by incentivizing operators

to keep older, higher-emitting trucks on the road for

longer), and would increase supply chain costs.

Greenhouse Gas Emission Standards

In October 2016, EPA and NHTSA jointly published the

current set of GHG emission and fuel efficiency standards

for medium- and heavy-duty vehicles and engines (81

Federal Register 73478) through their authorities under the

CAA and the Energy Independence and Security Act of

2007 (EISA, P.L. 110-140). These standards, referred to as

Phase 2, expanded on the Phase 1 standards (promulgated

in September 2011, for MY2014 through MY2018; 76

Federal Register 57106) and introduced first-ever controls

on trailers (the part of the vehicle pulled by the tractor—

since vacated) and glider vehicles (a new chassis combined

with an older engine). The standards phase-in between

MY2021 and MY2027 for engines and vehicles and

between MY2018 and MY2027 for gliders (see Figure 1).

The Phase 2 rule maintained the underlying regulatory

structure developed in Phase 1, such as the general

categorization of medium- and heavy-duty vehicles and the

separate standards for engines and vehicles. It also retained

the Phase 1 averaging, banking, and trading compliance

provisions and its flexibilities for small businesses.

However, unlike Phase 1, the rule established “technologyadvancing standards”—standards based not only on

currently available technologies but also on utilization of

technologies under development or not widely deployed.

These could include advancements in the engine,

transmission, driveline, aerodynamic design, lower rolling

resistance tires, and extended idle reduction technologies.

The Phase 3 proposal, announced in Executive Order

14037, is scheduled for release in the spring of 2023.

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Heavy-Duty Vehicles, Air Pollution, and Climate Change

Figure 1. CO2 and Fuel Consumption Reductions from the Phase 2 Medium- and Heavy-Duty Vehicle Standards

Source: Courtesy of International Council on Clean Transportation, under a Share Alike license of Creative Commons.

Notes: Classifications defined at 49 C.F.R. §523.2 and 49 C.F.R. §565.15.

Selected Issues

Some selected issues from the Phase 2 GHG rulemaking

that have remained of interest to Congress include the

following:

Trailer Provisions

The Phase 2 rule included standards for both engine

emissions and the vehicle as a whole, including

requirements for improvements to the aerodynamics of

freight trailers. In November 2021, the U.S. Court of

Appeals for the D.C. Circuit granted the Truck Trailer

Manufacturing Association’s petition for review, holding

that EPA cannot regulate trailers under CAA Section 202(a)

because trailers are not “self-propelled” motor vehicles. A

majority of the three-judge panel also held that NHTSA

does not have authority to regulate trailers under EISA

because trailers use no fuel.

Racecar Provisions

In the Phase 2 proposal, EPA included language that was

intended to clarify tampering provisions with respect to

nonroad vehicles. Industry groups claimed that the

provisions would prevent owners from modifying motor

vehicles used exclusively for racing. EPA removed the

language from the final rule. Nevertheless, some argue that

the underlying compliance uncertainty remains. Legislation

to clarify it has been proposed in several Congresses (most

recently H.R. 3281/S. 2736 in the 117th Congress). In

December 2016, the Racing Enthusiasts and Suppliers

Coalition filed a petition with the D.C. Circuit to address

the uncertainty. On August 12, 2022, the three-judge panel

dismissed the petition for review.

Glider Kit and Glider Vehicle Provisions

The term glider kit is used in the vehicle industry to

describe a chassis and cab assembly that is produced

without a new engine, transmission, or rear axle. A third

party then typically installs used parts to complete the

assembly. Historically, gliders have been used as a means

to salvage valuable components from vehicles that were

badly damaged in collisions. Prior to the Phase 2

rulemaking, EPA and NHTSA observed a sharp increase in

glider sales, suggesting to them that gliders were being used

to circumvent standards for safety and emissions (e.g., NOx

and particulates). For this reason, EPA moved to apply

current emission standards to gliders under the Phase 2 rule.

In July 2017, several glider kit manufacturers filed a

petition for reconsideration with EPA, arguing that gliders

should not be considered “new motor vehicles” under the

CAA, and that EPA thus lacked the authority to regulate

them. In November 2017, EPA issued a proposed repeal of

the requirements (82 Federal Register 53442). Upon

review, the White House Office of Information and

Regulatory Affairs reportedly informed EPA that the

agency needed a regulatory impact analysis before it could

finalize the repeal. In July 2018, EPA announced an 18month enforcement pause on the Phase 2 production limits

for glider vehicles as it reconsidered the rule. No further

action has been taken since.

Richard K. Lattanzio, Specialist in Environmental Policy

https://crsreports.congress.gov

IF12043

Heavy-Duty Vehicles, Air Pollution, and Climate Change

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https://crsreports.congress.gov | IF12043 · VERSION 5 · UPDATED