Updated May 9, 2022
Heavy-Duty Vehicles, Air Pollution, and Climate Change
On August 5, 2021, the Biden Administration announced
devices or comparably effective advanced technologies.
plans to reduce greenhouse gas (GHG) emissions and other
Because many of these devices are damaged by sulfur, EPA
air pollutants from medium- and heavy-duty vehicles and
simultaneously promulgated a new fuel standard. The fuel
engines through a series of rulemakings over three years
standard limited the sulfur content in on-highway diesel
(Executive Order 14037, “Strengthening American
fuel to 15 parts per million (ppm), down from the previous
Leadership in Clean Cars and Trucks,” 86 Federal Register
500 ppm. Refiners were required to start producing the 15
43583). The first rule, to be promulgated by the U.S.
ppm “ultra-low sulfur diesel” (ULSD) fuel beginning in
Environmental Protection Agency (EPA) and slated to be
June 2006. The MY2007 rule provided flexibilities for
finalized in 2022, applies to heavy-duty vehicles starting in
refiners, especially small refiners, and for manufacturers of
model year (MY) 2027. The rule would set new standards
engines and vehicles, to aid them in implementing the new
for nitrogen oxides (NOx) emissions for the sector as well
requirements in the most cost-efficient manner.
as targeted updates to the current GHG emission standards.
A second rule, to be promulgated by EPA and the National
Phase 2 GHG Standards
Highway Traffic Safety Administration (NHTSA), would
In October 2016, EPA and NHTSA jointly published the
set more stringent GHG emission and fuel efficiency
current, second phase of GHG emission and fuel efficiency
standards for new medium- and heavy-duty vehicles and
standards for medium- and heavy-duty vehicles and engines
engines beginning with MY2030.
(81 Federal Register 73478) through their authorities under
the CAA and the Energy Independence and Security Act of
Emissions from Heavy-Duty Vehicles
2007 (EISA, P.L. 110-140). The rule expanded on the
The medium- and heavy-duty vehicle and engine sector
Phase 1 standards (promulgated in September 2011, for
(defined at 40 C.F.R. §1037 and 49 C.F.R. §523) generally
MY2014 through MY2018; 76 Federal Register 57106)
includes tractor-trailers, vocational vehicles, buses, and
and introduced first-ever controls on trailers (the part of the
heavy-duty pickup trucks and vans. EPA reports that
vehicle pulled by the tractor—since vacated) and glider
“pollution from heavy-duty trucks contributes to poor air
vehicles (a new chassis combined with an older engine).
quality and health across the country, especially in
The standards phase in between MY2021 and MY2027 for
overburdened and underserved communities.” These
engines and vehicles and between MY2018 and MY2027
vehicles are the largest contributor to mobile source
for gliders.
emissions of NOx (about 32% in 2017). NOx reacts in the
atmosphere to form ground-level ozone (i.e., smog) and
The Phase 2 rule maintained the underlying regulatory
particulate matter (i.e., soot). Further, according to EPA’s
structure developed in Phase 1, such as the general
Inventory of U.S. Greenhouse Gas Emissions and Sinks:
categorization of medium- and heavy-duty vehicles and the
1990–2019 (published April 2021), medium- and heavy-
separate standards for engines and vehicles. It also retained
duty vehicles emitted 456.6 million metric tons of carbon
the Phase 1 averaging, banking, and trading compliance
dioxide (CO2) in 2019 (about 25% of total CO2 emissions
provisions and its flexibilities for small businesses.
from the U.S. transportation sector).
However, unlike Phase 1, the rule established “technology-
advancing standards”—standards based “not only on
Current Standards
currently available technologies but also on utilization of
MY2007 Emission Standards
technologies now under development or not yet widely
deployed.” These could include advancements in the
In January 2001, EPA finalized the current set of emission
engine, transmission, driveline, aerodynamic design, lower
standards for criteria, or common, pollutants from heavy-
rolling resistance tires, and extended idle reduction
duty vehicles and engines (66 Federal Register 5002)
technologies.
through its authorities under the Clean Air Act (CAA). The
rule included two components: (1) MY2007 and later
MY2027 Proposal
medium- and heavy-duty engine emission standards, and
On March 28, 2022, EPA proposed new heavy-duty vehicle
(2) diesel fuel regulations.
and engine emission standards for MY2027 and later (87
Federal Register 17414) as required by Executive Order
The emission standards included new, more stringent limits
14037. The proposal would strengthen the heavy-duty NOx
for particulate matter (0.01 grams per brake horsepower-
standard (a 50% to 90% reduction from the existing
hour (g/bhp·hr, a unit of work)) and NOx (0.20 g/bhp·hr)—
standard, depending upon the proposed option, MY, engine
an approximately 90% reduction from the prior standards.
type, and duty cycle) and adopt new requirements for
The particulate matter emission standard took full effect in
engine test cycle, regulatory useful life, emission-related
MY2007. The NOx standard was phased in between
warranty, and other requirements. Further, the proposal
MY2007 and MY2010. The standards were based on the
would make targeted adjustments to the Phase 2 GHG
use of high-efficiency catalytic exhaust emission control
standards based on future sales projections.
https://crsreports.congress.gov

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Heavy-Duty Vehicles, Air Pollution, and Climate Change
Figure 1. CO2 and Fuel Consumption Reductions from the 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
Glider Kit and Glider Vehicle Provisions
Some selected issues from the Phase 2 GHG rulemaking
The term glider kit is used in the vehicle industry to
that have remained of interest to Congress include the
describe a chassis and cab assembly that is produced
following:
without a new engine, transmission, or rear axle. A third
party then typically installs used parts to complete the
Trailer Provisions
assembly. Historically, gliders have been used as a means
The Phase 2 rule included standards for both engine
to salvage valuable components from vehicles that were
emissions and the vehicle as a whole, including
badly damaged in collisions. Prior to the Phase 2
requirements for improvements to the aerodynamics of
rulemaking, EPA and NHTSA observed a sharp increase in
freight trailers. In November 2021, the U.S. Court of
glider sales, suggesting to them that gliders were being used
Appeals for the D.C. Circuit granted the Truck Trailer
to circumvent standards for safety and emissions (e.g., NOx
Manufacturing Association’s petition for review, holding
and particulates). For this reason, EPA moved to apply
that EPA cannot regulate trailers under CAA Section 202(a)
current emission standards to gliders under the Phase 2 rule.
because trailers are not “self-propelled” motor vehicles. A
majority of the three-judge panel also held that NHTSA
In July 2017, several glider kit manufacturers filed a
does not have authority to regulate trailers under EISA
petition for reconsideration with EPA, arguing that gliders
because trailers use no fuel.
should not be considered “new motor vehicles” under the
CAA, and that EPA thus lacked the authority to regulate
Racecar Provisions
them. In November 2017, EPA issued a proposed repeal of
In the Phase 2 proposal, EPA included language that was
the requirements (82 Federal Register 53442). Upon
intended to clarify tampering provisions with respect to
review, the White House Office of Information and
nonroad vehicles. Industry groups claimed that the
Regulatory Affairs reportedly informed EPA that the
provisions would prevent owners from modifying motor
agency needed a regulatory impact analysis before it could
vehicles used exclusively for racing. EPA removed the
finalize the repeal. In July 2018, EPA announced an 18-
language from the final rule. Nevertheless, some argue that
month enforcement pause on the Phase 2 production limits
the underlying compliance uncertainty remains. Legislation
for glider vehicles as it reconsidered the rule. No further
to clarify it has been proposed in several Congresses (most
action has been taken.
recently H.R. 3281/S. 2736 in the 117th Congress). In
December 2016, the Racing Enthusiasts and Suppliers
Richard K. Lattanzio, Specialist in Environmental Policy
Coalition filed a petition with the D.C. Circuit to address
IF12043
the uncertainty. Final briefs in the case are due on March
30, 2022.
https://crsreports.congress.gov

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Heavy-Duty Vehicles, Air Pollution, and Climate Change


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https://crsreports.congress.gov | IF12043 · VERSION 3 · UPDATED

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