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February 11, 2022
Heavy-Duty Vehicles, Air Pollution, and Climate Change
On August 5, 2021, the Biden Administration announced
use of high-efficiency catalytic exhaust emission control
plans to reduce greenhouse gas (GHG) emissions and other
devices or comparably effective advanced technologies.
air pollutants from medium- and heavy-duty vehicles and
Because many of these devices are damaged by sulfur, EPA
engines through a series of rulemakings over three years
simultaneously promulgated a new fuel standard. The fuel
(Executive Order 14037, “Strengthening American
standard limited the sulfur content in on-highway diesel
Leadership in Clean Cars and Trucks,” 86 Federal Register
fuel to 15 parts per million (ppm), down from the previous
43583). The first rule, to be promulgated by the U.S.
500 ppm. Refiners were required to start producing the 15
Environmental Protection Agency (EPA) and slated to be
ppm “ultra-low sulfur diesel” (ULSD) fuel beginning in
finalized in 2022, applies to heavy-duty vehicles starting in
June 2006. The MY2007 rule provided flexibilities for
model year (MY) 2027. The rule would set new standards
refiners, especially small refiners, and for manufacturers of
for nitrogen oxides (NOx) emissions for the sector as well
engines and vehicles, to aid them in implementing the new
as targeted updates to the current GHG emission standards.
requirements in the most cost-efficient manner.
A second rule, to be promulgated by EPA and the National
Highway Traffic Safety Administration (NHTSA), would
Phase 2 GHG Standards
set more stringent GHG emission and fuel efficiency
In October 2016, EPA and NHTSA jointly published the
standards for new medium- and heavy-duty vehicles and
current, second phase of GHG emission and fuel efficiency
engines beginning with MY2030.
standards for medium- and heavy-duty vehicles and engines
(81 Federal Register 73478) through their authorities under
Emissions from Heavy-Duty Vehicles
the CAA and the Energy Independence and Security Act of
The medium- and heavy-duty vehicle and engine sector
2007 (EISA, P.L. 110-140). The rule expanded on the
(defined at 40 C.F.R. §1037 and 49 C.F.R. §523) generally
Phase 1 standards (promulgated in September 2011, for
includes tractor-trailers, vocational vehicles, buses, and
MY2014 through MY2018; 76 Federal Register 57106)
heavy-duty pickup trucks and vans. EPA reports that
and introduced first-ever controls on trailers (the part of the
“pollution from heavy-duty trucks contributes to poor air
vehicle pulled by the tractor—since vacated) and glider
quality and health across the country, especially in
vehicles (a new chassis combined with an older engine).
overburdened and underserved communities.” These
The standards phase in between MY2021 and MY2027 for
vehicles are the largest contributor to mobile source
engines and vehicles and between MY2018 and MY2027
emissions of NOx (about 32% in 2017). NOx reacts in the
for gliders. The agencies outlined several benefits of the
atmosphere to form ground-level ozone (i.e., smog) and
rule, including (1) reducing CO2 emissions and fuel
particulate matter (i.e., soot). Further, according to EPA’s
consumption from new vehicles, (2) reducing the costs for
Inventory of U.S. Greenhouse Gas Emissions and Sinks:
transporting goods, and (3) spurring innovation in the
1990–2019 (published April 2021), medium- and heavy-
energy technology sector.
duty vehicles emitted 456.6 million metric tons of carbon
dioxide (CO2) in 2019 (about 25% of total CO2 emissions
The Phase 2 rule maintained the underlying regulatory
from the U.S. transportation sector).
structure developed in Phase 1, such as the general
categorization of medium- and heavy-duty vehicles and the
Current Standards
separate standards for engines and vehicles. It also retained
the Phase 1 averaging, banking, and trading compliance
MY2007 Emission Standards
provisions and its flexibilities for small businesses.
In January 2001, EPA finalized the current set of emission
However, unlike Phase 1, the rule established “technology-
standards for criteria, or common, pollutants from heavy-
advancing standards”—standards based “not only on
duty vehicles and engines (66 Federal Register 5002)
currently available technologies but also on utilization of
through its authorities under the Clean Air Act (CAA). The
technologies now under development or not yet widely
rule included two components: (1) MY2007 and later
deployed.” These could include advancements in the
medium- and heavy-duty engine emission standards, and
engine, transmission, driveline, aerodynamic design, lower
(2) diesel fuel regulations.
rolling resistance tires, and extended idle reduction
technologies. The agencies estimated that the Phase 2
The emission standards included new, more stringent limits
standards would achieve vehicle fuel savings of up to 25%
for particulate matter (0.01 grams per brake horsepower-
beyond Phase 1 when fully implemented (see Figure 1).
hour (g/bhp·hr, a unit of work)) and NOx (0.20 g/bhp·hr)—
Overall, the agencies estimated that the standards would
an approximately 90% reduction from the prior standards.
cost the affected industry approximately $30 billion, could
The particulate matter emission standard took full effect in
cut GHG emissions by 1.1 billion metric tons of CO2,
MY2007. The NOx standard was phased in between
conserve 2 billion barrels of oil, and save vehicle owners an
MY2007 and MY2010. The standards were based on the
https://crsreports.congress.gov
Heavy-Duty Vehicles, Air Pollution, and Climate Change
estimated $170 billion in fuel costs over the lifetime of the
vehicles sold in the regulatory time frame.
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
Coalition filed a petition with the D.C. Circuit to address
Some selected issues from the Phase 2 GHG rulemaking
the uncertainty. Final briefs in the case are due on March
that have remained of interest to Congress include:
30, 2022.
Trailer Provisions
Glider Kit and Glider Vehicle Provisions
The Phase 2 rule included standards for both engine
The term glider kit is used in the vehicle industry to
emissions and the vehicle as a whole, including
describe a chassis and cab assembly that is produced
requirements for improvements to the aerodynamics of
without a new engine, transmission, or rear axle. A third
freight trailers. In November 2021, the U.S. Court of
party then typically installs used parts to complete the
Appeals for the D.C. Circuit granted the Truck Trailer
assembly. Historically, gliders have been used as a means
Manufacturing Association’s petition for review, holding
to salvage valuable components from vehicles that were
that EPA cannot regulate trailers under CAA Section 202(a)
badly damaged in collisions. Prior to the Phase 2
because trailers are not “self-propelled” motor vehicles. A
rulemaking, EPA and NHTSA observed a sharp increase in
majority of the three-judge panel also held that NHTSA
glider sales, suggesting to them that gliders were being used
does not have authority to regulate trailers under EISA
to circumvent standards for safety and emissions (e.g., NOx
because trailers use no fuel.
and particulates). For this reason, EPA moved to apply
current emission standards to gliders under the Phase 2 rule.
Racecar Provisions
In the Phase 2 proposal, EPA included language that was
In July 2017, several glider kit manufacturers filed a
intended to clarify tampering provisions with respect to
petition for reconsideration with EPA, arguing that gliders
nonroad vehicles. Industry groups claimed that the
should not be considered “new motor vehicles” under the
provisions would prevent owners from modifying motor
CAA, and that EPA thus lacked the authority to regulate
vehicles used exclusively for racing. EPA removed the
them. In November 2017, EPA issued a proposed repeal of
language from the final rule. Nevertheless, some argue that
the requirements (82 Federal Register 53442). Upon
the underlying compliance uncertainty remains. Legislation
review, the White House Office of Information and
to clarify it has been proposed in several Congresses (most
Regulatory Affairs reportedly informed EPA that the
recently H.R. 3281/S. 2736 in the 117th Congress). In
agency needed a regulatory impact analysis before it could
December 2016, the Racing Enthusiasts and Suppliers
finalize the repeal. In July 2018, EPA announced an 18-
https://crsreports.congress.gov
Heavy-Duty Vehicles, Air Pollution, and Climate Change
month enforcement pause on the Phase 2 production limits
Richard K. Lattanzio, Specialist in Environmental Policy
for glider vehicles as it reconsidered the rule. No further
action has been taken.
IF12043
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https://crsreports.congress.gov | IF12043 · VERSION 1 · NEW