Cars, Trucks, and Climate: EPA Regulation of
Greenhouse Gases from Mobile Sources
James E. McCarthy
Specialist in Environmental Policy
Brent D. Yacobucci
Section Research Manager
February 14, 2013
Congressional Research Service
7-5700
www.crs.gov
R40506
CRS Report for Congress
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Summary
On October 15, 2012, the Obama Administration took a major step toward reducing greenhouse
gas (GHG) emissions from motor vehicles when it promulgated GHG emission standards for
model year 2017-2025 light duty vehicles. Under the standards, GHG emissions from new cars
and light trucks will be reduced about 50% by 2025 compared to 2010, and average fuel economy
standards will rise to nearly 50 miles per gallon. EPA had previously set GHG emission standards
for MY2012-2016 vehicles as well as for 2014-2018 model year medium- and heavy-duty trucks.
These steps have been taken as the Congress (particularly the House) and the Administration have
reached an impasse over climate issues. The Administration has made clear that its preference
would be for Congress to address the climate issue through new legislation. Nevertheless, in the
wake of a 2007 Supreme Court decision, it has moved forward on several fronts to define how the
Clean Air Act will be used and to promulgate regulations.
The key to using the CAA’s authority to control greenhouse gases was for the EPA Administrator
to find that GHG emissions are air pollutants that endanger public health or welfare. EPA
Administrator Jackson promulgated such an endangerment finding in December 2009. With the
endangerment finding finalized, the agency has proceeded to regulate emissions from motor
vehicles.
In all, EPA has received 12 petitions asking that it make endangerment findings and proceed to
regulate emissions of greenhouse gases. Ten of the 12 petitions addressed mobile sources: besides
motor vehicles, the petitions cover aircraft, ships, nonroad vehicles and engines, locomotives, and
fuels, all of which are covered by Title II of the CAA. This report discusses the full range of
EPA’s authority under Title II and provides information regarding other mobile sources that might
be regulated under this authority, in addition to describing the car and truck regulations.
Regulation of GHGs from mobile sources has led the agency to establish controls for stationary
sources, such as electric power plants, as well. Stationary source options, the authority for which
comes from different parts of the CAA, are addressed in CRS Report R41212, EPA Regulation of
Greenhouse Gases: Congressional Responses and Options.








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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Contents
Introduction ...................................................................................................................................... 1
Massachusetts v. EPA and Its Effects ............................................................................................... 1
Standards for New Light-Duty Motor Vehicles ............................................................................... 3
Other Mobile Sources ...................................................................................................................... 5
Medium and Heavy-Duty Trucks .............................................................................................. 7
Ships ........................................................................................................................................ 10
Other Nonroad Engines ........................................................................................................... 12
Locomotives ............................................................................................................................ 14
Aircraft .................................................................................................................................... 14
Fuels ........................................................................................................................................ 16
Conclusion ..................................................................................................................................... 17

Figures
Figure 1. Motor Vehicle Greenhouse Gas Emissions ...................................................................... 4
Figure 2. Growth of GHG Emissions from Mobile Sources, 1990-2008 ........................................ 8

Tables
Table 1. Petitions for Regulation of Greenhouse Gas Emissions Under the Clean Air Act ............. 6
Table 2. Motor Vehicle GHG Emissions, 2008, by Source Category .............................................. 7
Table 3. Nonroad Sector CO2 Emissions, 2007, by Source Category............................................ 13
Table 4. Categories of Sources Whose GHG Emissions Can Be Regulated Under Title II
of the Clean Air Act .................................................................................................................... 18

Contacts
Author Contact Information........................................................................................................... 19

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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Introduction
Although much of the discussion of climate legislation has focused on cap-and-trade1 and tax
options,2 establishing greenhouse gas controls is not simply a choice between those two
alternatives. A third set of options, using the more traditional regulatory approaches of the Clean
Air Act (CAA), is available. These regulatory approaches could be modified through new
legislation, but unlike a cap-and-trade system or a carbon tax, regulation does not require new
congressional action: the ability to limit greenhouse gas (GHG) emissions already exists under
various CAA authorities that Congress has enacted, a point underlined by the Supreme Court in
an April 2007 decision, Massachusetts v. EPA.3
Thus, while the 111th Congress and the Administration discussed new legal authority (for cap-
and-trade, carbon tax, and/or targeted emission controls) the Administration, through the
Environmental Protection Agency (EPA), proceeded to exercise existing authority under the CAA
to begin regulation of greenhouse gas emissions.
The agency has taken several steps to regulate GHG emissions. Nevertheless, EPA Administrator
Jackson and others in the Administration have made clear that their preference would be for
Congress to address the climate issue through broad legislation. In an April 2009 press release,
for example, the agency stated, “notwithstanding this required regulatory process, both President
Obama and Administrator Jackson have repeatedly indicated their preference for comprehensive
legislation to address this issue and create the framework for a clean energy economy.”4 Similar
statements have been made on several occasions since that time; in the meantime, though, the
agency has concluded that current law, including the 2007 Supreme Court decision discussed
below, compels the agency to act.
This report focuses on EPA’s completed and potential actions regarding regulation of GHG
emissions from mobile sources under Title II of the CAA. We begin with a brief discussion of the
petitions and court action that have led to EPA’s regulatory decisions.
Massachusetts v. EPA and Its Effects
Whether EPA could regulate GHGs through existing CAA authority was under consideration at
EPA for more than a decade before the agency took action. In 1998, during the Clinton
Administration, EPA General Counsel Jonathan Cannon concluded in a memorandum to the
agency’s Administrator that greenhouse gases were air pollutants within the CAA’s definition of
the term, and therefore could be regulated under the act.5 Relying on the Cannon memorandum as

1 For a more detailed discussion of cap-and-trade approaches to GHG emission control, see CRS Report RL33799,
Climate Change: Design Approaches for a Greenhouse Gas Reduction Program.
2 For a more detailed discussion of a carbon tax approach to GHG emission control, see CRS Report R40242, Carbon
Tax and Greenhouse Gas Control: Options and Considerations for Congress.
3 For a discussion of the Court’s decision, see CRS Report RS22665, The Supreme Court’s Climate Change Decision:
Massachusetts v. EPA.
4 “EPA Finds Greenhouse Gases Pose Threat to Public Health, Welfare / Proposed Finding Comes in Response to 2007
Supreme Court Ruling,” Press Release, April 17, 2009, at http://yosemite.epa.gov/opa/admpress.nsf/
d0cf6618525a9efb85257359003fb69d/0ef7df675805295d8525759b00566924.
5 Memorandum from Jonathan Z. Cannon, EPA General Counsel, to Carol M. Browner, EPA Administrator, “EPA’s
(continued...)
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

well as the statute itself, on October 20, 1999, a group of 19 organizations petitioned EPA to
regulate greenhouse gas emissions from new motor vehicles under Section 202 of the act.6
Section 202 gives the EPA Administrator broad authority to set “standards applicable to the
emission of any air pollutant from any class or classes of new motor vehicles” if in her judgment
they cause or contribute to air pollution which “may reasonably be anticipated to endanger public
health or welfare.”
Under the Bush Administration, EPA denied the petition August 28, 2003,7 on the basis of a new
General Counsel memorandum the same day, in which it concluded that the CAA does not grant
EPA authority to regulate carbon dioxide (CO2) and other GHG emissions based on their climate
change impacts.8 The denial was challenged by Massachusetts, 11 other states, and various other
petitioners in a case that ultimately reached the Supreme Court. In an April 2, 2007, decision
(Massachusetts v. EPA), the Court found by 5-4 that EPA does have authority to regulate
greenhouse gas emissions, since the emissions are clearly air pollutants under the CAA’s
definition of that term.9 The Court’s majority concluded that EPA must, therefore, decide whether
emissions of these pollutants from new motor vehicles contribute to air pollution that may
reasonably be anticipated to endanger public health or welfare, or provide a reasonable
explanation why it cannot or will not make that decision, such as that there is insufficient
information to make the decision. When it makes such a finding of endangerment, the act requires
the agency to establish standards for emissions of the pollutants.10
In nearly two years following the Court’s decision, the Bush Administration’s EPA did not
respond to the original petition or make a finding regarding endangerment. Its only formal action
following the Court decision was to issue a detailed information request, called an Advance
Notice of Proposed Rulemaking (ANPR), on July 30, 2008.11

(...continued)
Authority to Regulate Pollutants Emitted by Electric Power Generation Sources,” April 10, 1998.
6 The lead petitioner was the International Center for Technology Assessment (ICTA). The petition may be found on
their website at http://www.icta.org/doc/ghgpet2.pdf.
7 The agency argued that it lacked statutory authority to regulate greenhouse gases: Congress “was well aware of the
global climate change issue” when it last comprehensively amended the CAA in 1990, according to the agency, but “it
declined to adopt a proposed amendment establishing binding emissions limitations.” Massachusetts v. EPA, 549 U.S.
497 (2007).
8 Memorandum from Robert E. Fabricant, EPA General Counsel, to Marianne L. Horinko, EPA Acting Administrator,
“EPA’s Authority to Impose Mandatory Controls to Address Global Climate Change Under the Clean Air Act,” August
28, 2003.
9 Massachusetts v. EPA, 549 U.S. 497 (2007). The majority held: “The Clean Air Act’s sweeping definition of ‘air
pollutant’ includes ‘any air pollution agent or combination of such agents, including any physical, chemical ...
substance or matter which is emitted into or otherwise enters the ambient air.... ’ ... Carbon dioxide, methane, nitrous
oxide, and hydrofluorocarbons are without a doubt ‘physical [and] chemical ... substances[s] which [are] emitted into ...
the ambient air.’ The statute is unambiguous.”
10 For further discussion of the Court’s decision, see CRS Report RS22665, The Supreme Court’s Climate Change
Decision: Massachusetts v. EPA.
11 U.S. EPA, “Regulating Greenhouse Gas Emissions Under the Clean Air Act,” 73 Federal Register 44354, July 30,
2008. The ANPR occupied 167 pages of the Federal Register. Besides requesting information, it took the unusual
approach of presenting statements from the Office of Management and Budget, four Cabinet Departments (Agriculture,
Commerce, Transportation, and Energy), the Chairman of the Council on Environmental Quality, the Director of the
President’s Office of Science and Technology Policy, the Chairman of the Council of Economic Advisers, and the
Chief Counsel for Advocacy at the Small Business Administration, each of whom expressed their objections to
regulating greenhouse gas emissions under the CAA. The OMB statement began by noting that, “The issues raised
during interagency review are so significant that we have been unable to reach interagency consensus in a timely way,
(continued...)
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

The Obama Administration’s EPA, however, made review of the endangerment issue a high
priority. On April 17, 2009, it proposed a finding that GHGs do endanger both public health and
welfare and that GHGs from new motor vehicles contribute to that endangerment.12 These
findings were finalized in the December 15, 2009 Federal Register.13
Standards for New Light-Duty Motor Vehicles
The proposed endangerment finding of April 2009 was followed in a matter of weeks by an
announcement that the Administration had reached agreement with nine auto manufacturers14 and
California (which had developed its own GHG emission standards for motor vehicles), as well as
other interested parties regarding the major outlines of a joint greenhouse gas/fuel economy
rulemaking. As announced by the President, May 19, 2009, EPA and the National Highway
Traffic Safety Administration (which administers fuel economy standards for cars and trucks)
would integrate corporate average fuel economy (CAFE) standards for new cars and light trucks
(collectively known as “light-duty motor vehicles”) with national greenhouse gas emission
standards to be issued by EPA. The objective of the joint standards was to achieve GHG reduction
levels similar to those adopted by California, which harmonized its own standards with EPA’s as
part of the agreement.15
Four greenhouse gases are emitted by motor vehicles (CO2, methane, nitrous oxide, and
hydrofluorocarbons).16 According to EPA, emissions of the four gases from motor vehicles
(including trucks) accounted for 23.6% of the total inventory of U.S. GHG emissions in 2006.
Most of the emissions are in the form of CO2 (see Figure 1), which is the product of combusting
any fuel containing carbon. Hydrofluorocarbons (HFCs), the chemicals used as coolants in
vehicle air conditioning systems, are the second-most important motor vehicle GHG; but, as the
figure shows, they are a distant second.

(...continued)
and as a result, this staff draft cannot be considered Administration policy or representative of the views of the
Administration.” (p. 44356) It went on to state that “... the Clean Air Act is a deeply flawed and unsuitable vehicle for
reducing greenhouse gas emissions.” The other letters concurred. The ANPR, therefore, was of limited use in reaching
a conclusion on the endangerment issue.
12 U.S. EPA, “Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a)
of the Clean Air Act,” 74 Federal Register 18886, April 24, 2009.
13 74 Federal Register 66496. Although generally referred to as simply “the endangerment finding,” the EPA
Administrator actually finalized two separate findings: a finding that six greenhouse gases endanger public health and
welfare, and a separate “cause or contribute” finding that the combined emissions of greenhouse gases from new motor
vehicles and new motor vehicle engines contribute to the greenhouse gas pollution that endangers public health and
welfare.
14 Letters containing those agreements may be accessed at http://www.epa.gov/otaq/climate/proposedregs.htm#cl.
15 74 Federal Register 49468, September 28, 2009.
16 Two other commonly mentioned greenhouse gases, sulfur hexafluoride (SF6) and perfluorocarbons, are not emitted
by motor vehicles.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Figure 1. Motor Vehicle Greenhouse Gas Emissions

Source: U.S. EPA, March 6, 2009 Draft Deliberative Presentation.
Notes: Motor vehicles = passenger cars, light duty trucks, other trucks, buses, and motorcycles, including
releases of HFCs from motor vehicle air conditioning. MMT=million metric tons; CO2 Eq.=carbon dioxide
equivalent; CH4=methane; N2O=nitrous oxide; HFCs=hydrofluorocarbons.
The EPA/NHTSA joint regulations for light-duty motor vehicles were finalized April 1, 2010.
They require the vehicles (cars, SUVs, minivans, and other light trucks) to meet combined
emissions levels that EPA estimates will average 250 grams/mile of CO2 in model year 2016,
about a 30% reduction in emissions compared to then-current levels. NHTSA set corresponding
fuel economy standards, achieving a combined estimated fuel economy of 34.1 miles per gallon
for cars and light trucks by 2016. In both cases, the standards are being gradually phased in, with
the first reduction targets set for model year 2012.
In setting the GHG standards, EPA used the concept of a vehicle’s “footprint” to set differing
standards for different size vehicles. As explained by EPA,
These standards are based on CO2 emissions-footprint curves, where each vehicle has a
different CO2 emissions compliance target depending on its footprint value (related to the
size of the vehicle). Generally, the larger the vehicle footprint, the higher the corresponding
vehicle CO2 emissions target. As a result, the burden of compliance is distributed across all
vehicles and all manufacturers. Manufacturers are not compelled to build light vehicles of
any particular size or type, and each manufacturer will have its own standard which reflects
the vehicles it chooses it [sic] produce.17
(For a further discussion of vehicle footprints and fuel economy standards, see CRS Report
R42721, Automobile and Truck Fuel Economy (CAFE) and Greenhouse Gas Standards.)
In general, manufacturers are expected to reduce CO2 emissions by improving the vehicles’ fuel
economy, but they can also take advantage of options to generate CO2-equivalent credits by

17 “EPA and NHTSA Finalize Historic National Program to Reduce Greenhouse Gases and Improve Fuel Economy for
Cars and Trucks,” Fact Sheet, April 2010, p. 3, at http://epa.gov/oms/climate/regulations/420f10014.pdf.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

reducing emissions of hydrofluorocarbons (HFCs) and CO2 through improvements in their air
conditioner systems or by the use of idle reduction technologies, among other strategies.
Manufacturers will also be allowed to average, bank, and trade emission credits.18
On October 15, 2012, EPA promulgated a second phase of GHG emission standards, for
MY2017-2025 light duty vehicles. Like the earlier standards, these were preceded by a multi-
party agreement, brokered by the White House, that included 13 auto manufacturers, the United
Auto Workers, the state of California, and other interested parties. The manufacturers agreed to
reduce GHG emissions from new cars and light trucks by about 50% by 2025, compared to 2010,
with fuel economy standards rising to nearly 50 miles per gallon. CO2 emissions will be reduced
to about 160 grams/mile by 2025, under the agreement.19
The light-duty vehicle rules affect a large group of emission sources that accounts for a
significant percentage of total U.S. GHG emissions, but the effectiveness of the standards in
reducing total GHG emissions is limited in that they will apply only to new motor vehicles. The
auto and light truck fleets turn over slowly: the median survival rate for 1990 cars, for example,
was 16.9 years, and that for light trucks was 15.5 years.20 Given this durability, the impact of
GHG standards on the total emissions of the motor vehicle fleet will take a long time to be felt. If
historic experience is any guide, much of the potential reduction in GHG emissions per new
vehicle may be offset by growth in vehicle miles traveled. That said, the Energy Information
Administration projects that under a CAFE scenario similar to that promulgated, light-duty
vehicle CO2 emissions will decrease by roughly 20% in 2030 from both the actual 2011 level and
the projected 2030 “business-as-usual” level.21
Other Mobile Sources
The endangerment finding and emission standards for new light-duty vehicles made it likely that
EPA would proceed to set GHG emission standards for other mobile sources of air pollution,
especially medium- and heavy-duty trucks. Since the Massachusetts v. EPA decision, the agency
has received eleven petitions asking it to regulate GHGs from other categories, all but two
focused on mobile sources and their fuels. These petitions cover aircraft, ocean-going ships and
their fuels, motor fuels in general, locomotives, and nonroad vehicles and engines—a category
that includes construction equipment, farm equipment, logging equipment, outdoor power
equipment, forklifts, marine vessels, recreational vehicles, and lawn and garden equipment.

18 For additional detail on the EPA/NHTSA joint standards, see CRS Report R42721, Automobile and Truck Fuel
Economy (CAFE) and Greenhouse Gas Standards
19 Environmental Protection Agency and National Highway Traffic Safety Administration, 2017-2025 Model Year
Light-Duty Vehicle GHG Emissions and CAFE Standards: Supplemental Notice of Intent, Washington, DC, July 29,
2011, at http://www.epa.gov/otaq/climate/regs-light-duty.htm#new1. The auto manufacturers’ letters of support can be
found at http://www.epa.gov/otaq/climate/letters.htm. The final emission standards are at EPA and NHTSA, “2017 and
Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards;
Final Rule,” 77 Federal Register 62624, October 15, 2012.
20 Oak Ridge National Laboratory, for the U.S. Department of Energy, Transportation Energy Data Book: Edition 27,
2008, Tables 3.10 and 3.11.
21 Under the previously promulgated standards for model years 2012-2016, EIA’s Reference Case projected that light-
duty vehicle CO2 emissions would drop below current levels until 2025, returning to current levels in 2030 and
growing beyond that. U.S. Energy Information Administration, Annual Energy Outlook 2011 Interactive Table Viewer,
Washington, DC, April 26, 2011, http://www.eia.gov/oiaf/aeo/tablebrowser/.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Table 1. Petitions for Regulation of Greenhouse Gas Emissions
Under the Clean Air Act
Date Subject
CAA
Section
Petitioner
10/20/99 New Motor Vehicles
202(a)(1)
International Center for Technology Assessment
(ICTA) and 19 other organizations




10/3/07
Ocean Going Vessels
213(a)(4)
California Attorney General
10/3/07
Marine Shipping Vessels and their
213(a)(4) and
Oceana, Friends of the Earth, and the Center for
Fuels
211
Biological Diversity (CBD)
1/10/08
New Marine Engines and Vessels
213(a)(4)
South Coast Air Quality Management District




12/5/07
Aircraft
231
States of California, Connecticut, New Jersey,
New Mexico, Pennsylvania, City of New York,
District of Columbia, South Coast Air Quality
Management District
12/5/07 Aircraft
Engines
231(a)(2)(A) Friends of the Earth, Oceana, CBD, and the
and 231(a)(3)
Natural Resources Defense Council




1/29/08
New Nonroad Vehicles and
202(a)(3)(D)
ICTA, Center for Food Safety, and Friends of the
Engines and Rebuilt Heavy-Duty
and 213(a)(4)
Earth
Engines, excluding Aircraft and
Vessels
1/29/08
New Nonroad Vehicles and
202 and
States of California, Connecticut, Massachusetts,
Engines, excluding Aircraft,
213(a)(4)
New Jersey, Oregon, and Pennsylvania
Locomotives, and Vessels




7/29/09
Fuels Used in Motor Vehicles,
211 and 231
NYU Law School Institute for Policy Integrity
Nonroad Vehicles, and Aircraft




9/21/09
Concentrated Animal Feeding
111(b) and (d)
Humane Society of the United States and 8 other
Operations
organizations
6/16/10
Coal Mines
111(b) and (d)
Earthjustice, Wild Earth Guardians, CBD,
Environmental Integrity Project, and Sierra Club
9/21/10
Locomotives
213(a)(5)
CBD, Friends of the Earth, and ICTA
Source: U.S. EPA and the petitioning organizations.
The specifics of the CAA sections that give EPA authority to regulate pollution from these
sources vary somewhat, but it is generally believed that the endangerment finding and decision to
regulate GHGs in response to the first of the petitions will make it difficult for the agency to
avoid regulating at least some of the other categories. With that in mind, we look at other mobile
source categories, the authorities provided under Title II for each, and what EPA’s use of these
authorities for conventional pollutants emitted by these sources indicates with regard to its ability
to regulate greenhouse gases. (A separate report, CRS Report R41212, EPA Regulation of
Greenhouse Gases: Congressional Responses and Options, discusses the potential CAA
regulatory tools for stationary sources.)
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Medium and Heavy-Duty Trucks
Section 202(a) of the CAA, the section that provided authority for the light-duty vehicle GHG
standards, requires the Administrator to set “standards applicable to the emission of any air
pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in
his judgment cause, or contribute to, air pollution which may reasonably be anticipated to
endanger public health or welfare” (emphasis added). This authority covers medium- and heavy-
duty trucks: in fact, the December 15, 2009, endangerment and cause-or-contribute findings
specifically identified the medium- and heavy-duty truck categories as among those that
contributed to the GHG emissions for which it found endangerment. As a result, EPA proposed
standards for these vehicles on October 25, 2010, and promulgated them on September 15,
2011.22
In addition, in the Energy Independence and Security Act of 2007 (EISA, P.L. 110-140), NHTSA
was directed to study the potential for fuel efficiency standards for medium- and heavy-duty
trucks, and, if feasible, set efficiency standards reflecting the “maximum feasible
improvement.”23 Thus, as with light duty vehicles, EPA and NHTSA have cooperated on the
setting of standards.
Table 2. Motor Vehicle GHG Emissions, 2008, by Source Category
(million metric tons, CO2-equivalent)
Total GHG
Percent of Motor
Category
Emissions
Vehicle Total
Passenger Cars
632.1
39.5%
Light Duty Trucks
552.4
34.5%
Medium- and Heavy-Duty Trucks
401.2
25.1%
Buses 12.1
0.8%
Motorcycles 2.2
0.1%
Total 1,600.0

Source: U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks, 1990-2008, Table 2-15.
Medium- and heavy-duty trucks are trucks with a gross vehicle weight of 10,000 pounds or more.
The largest emitters, tractor-trailers (Class 8b trucks), account for roughly 30% of the total
number of medium- and heavy-duty trucks, but, because they are heavier and are driven longer
distances, they consume 67% of all fuel used by these vehicles.24 Presumably, they emit about the
same percentage of all trucks’ GHGs. Box trucks, which tend to be lighter and are more
frequently used in urban settings, are a distant second in terms of GHG emissions. As shown in
Table 2, medium- and heavy-duty trucks emitted about 400 million metric tons of GHGs in 2008,
about 25% of GHG emissions from motor vehicles. Between 1990 and 2008, emissions from

22 U.S. Environmental Protection Agency, U.S. Department of Transportation, “Greenhouse Gas Emissions Standards
and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles; Final Rules,” 76 Federal Register
57106, September 15, 2011.
23 Section 102.
24 National Research Council, Technologies and Approaches to Reducing the Fuel Consumption of Medium- and
Heavy-Duty Vehicles, The National Academies Press, Washington, April 2010, Table 2-1.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

these trucks grew 74%, the fastest growth for any major category of GHG sources. (See Figure
2.)
Figure 2. Growth of GHG Emissions from Mobile Sources, 1990-2008
80%
74%
70%
60%
50%
40%
30%
30%
19%
20%
10%
0%
-10%
-13%
-20%
Aircraft
Cars/LDTs
Rail
Trucks

Source: U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks, 1990-2008, Table 2-15.
The EPA Administrator is given substantial leeway in the design and implementation of motor
vehicle regulations. The act states that the Administrator may establish categories for purposes of
regulation based on “gross vehicle weight, horsepower, type of fuel used or other appropriate
factors.” In addition, she may delay the effective date of regulations as long as she finds
necessary “to permit the development and application of the requisite technology, giving
appropriate consideration to the cost of compliance within such period.” Using this authority in
regulating conventional pollutants, EPA has used weight or power classifications to set differing
levels of emission standards, particularly for trucks; it has given manufacturers as much as four
years lead time to develop emission controls; and it has set different standards based on the type
of fuel an engine uses. Except for specific conventional pollutants mentioned in Section 202, the
act does not specify a level of stringency (e.g., best available control technology) for prospective
regulations.
Although flexible in many respects, motor vehicle standards have often been used to force the
development of new technology. In adopting technology-forcing regulations, EPA has generally
followed the lead of California. Because of its more severe air pollution and its pioneering role in
establishing motor vehicle emission control requirements in the 1960s, California is allowed to
adopt standards more stringent than federal requirements. The state must apply for a waiver of
federal preemption under CAA Section 209(b) in order to enforce its more stringent standards,
which EPA is to grant if the state meets certain criteria, primarily a showing that the standards are
needed to meet “compelling and extraordinary conditions.” If California is granted a waiver, other
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A Practical Guide to Parlaying an Understanding of Congressional
Folkways and Dynamics into Successful Advocacy on Capitol Hill
How to Spend
Less and Get More
from Congress:
Candid Advice
for Executives
By Joseph Gibson
Persuading
Congress

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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

states with air quality problems may adopt identical requirements, thus reinforcing the potential
impact of California’s technology-forcing standards.
EPA discussed several potential strategies for reducing GHG emissions from medium- and heavy-
duty trucks in its July 2008 Advance Notice of Proposed Rulemaking,25 including the following:
1. Improvements in Engine Technology. Most trucks, particularly tractor-trailers,
are powered by diesel engines, which are already quite efficient; but EPA thinks
that a number of small improvements (such as better lubricants and higher
cylinder pressure) could increase diesel engine efficiency by up to 20%. For
urban trucks, which engage in stop-and-go driving and may idle frequently in
traffic, hybrid engine technologies show promise of substantial reductions in
emissions.
2. Eliminating Aerodynamic Drag. Aerodynamic drag is an important factor in
fuel consumption, particularly for tractor-trailers. EPA estimates that drag
accounts for 21% of energy consumed by tractor-trailers at 65 miles per hour.
The agency has promoted a number of relatively simple redesigns (high roof
fairings, side skirts, side fairing gap reducers, aerodynamic mirrors and bumpers)
through its SmartWay voluntary program. These measures can have a significant
impact on fuel use.
3. Reducing Rolling Resistance. Tire rolling resistance accounts for about 13% of
energy consumed by tractor trailers, according to EPA. The agency says that 10%
or greater reductions in rolling resistance have already been demonstrated and
continued innovation has the potential to achieve larger improvements. In
addition to better tires with less rolling resistance, tire inflation indicators can
improve fuel efficiency.
4. Addressing Operational Factors. Operational factors refer to a wide variety of
measures that can reduce truck fuel use, including the installation of speed
governors (widely used in Europe and by some fleets in the United States).
According to EPA, vehicle speed is the single largest operational factor affecting
CO2 emissions from trucks: every one mile per hour increase above 55 mph
increases CO2 emissions by more than 1%. Engine idling is another operational
factor affecting fuel consumption and GHG emissions. The addition of auxiliary
power units or truck stop electrification could eliminate the need for extended
idling, reducing emissions.
All in all, EPA stated in its 2008 analysis of the issues, “we see a potential for up to a 40%
reduction in GHG emissions from a typical heavy-duty truck in the 2015 timeframe, with greater
reductions possible looking beyond 2015.... ”26
As noted earlier, EPA and NHTSA jointly promulgated GHG and fuel economy standards on
September 15, 2011. For a variety of reasons, including agency decisions not to address trailer
design issues, the promulgated standards will not achieve anywhere near the 40% reduction that
the agency found achievable in 2008.

25 U.S. EPA, “Regulating Greenhouse Gas Emissions Under the Clean Air Act,” Advance Notice of Proposed
Rulemaking, July 30, 2008, 73 Federal Register 44453-44458.
26 Ibid., p. 44454.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

The standards divide trucks into three main categories: (1) heavy-duty pickup trucks and vans; (2)
combination tractors (the power unit of a tractor-trailer combined vehicle); and (3) vocational
vehicles.27
The standards for heavy-duty pickups and vans use an approach similar to that for light duty
vehicles, in which each manufacturer would be required to meet an average standard that would
vary depending on its sales mix, with higher capacity vehicles (based on payload, towing
capacity, and 4-wheel drive) having less stringent targets. The standards, which will be phased in
from 2014 to 2018, are estimated by EPA to cut GHG emissions an average of 17% in diesel
vehicles when fully implemented in 2018, and 12% in comparable gasoline-powered vehicles,
compared to a model year 2010 baseline.28
For the other categories of trucks, referred to as vocational vehicles or combination tractors, the
standards vary significantly depending on the size of the truck. These standards are expected to
reduce GHG emissions up to 23% for combination tractors and 6% to 9% for vocational vehicles
by model year 2017, according to the final rule.29
In addition to engine emission standards, the proposal would set a standard for refrigerant leaks,
in order to address emissions of HFC greenhouse gases. But trailer design, a major source of
efficiency losses (and, thus, higher GHG emissions), is not addressed. According to EPA,
Trailers are not covered under this proposal, due to the first-ever nature of this proposal and
the agencies’ limited experience working in a compliance context with the trailer
manufacturing industry. However, because trailers do impact the fuel consumption and CO2
emissions from combination tractors, and because of the opportunities for reductions, we are
soliciting comments on controlling GHG emissions and fuel consumption from trailers, to
prepare a foundation for a possible future rulemaking.30
Ships
Three of the 12 petitions to EPA asking the agency to control greenhouse gas emissions concern
ocean-going ships (also referred to as marine engines and vessels) and (in two of the petitions)
their fuel. Although there is a wide range of estimates, the International Maritime Organization’s
consensus is that international shipping emitted 843 million metric tons of carbon dioxide, 2.7%
of global CO2 emissions in 2007. Including domestic shipping and fishing vessels larger than 100
gross tonnes, the amount would increase to 1.019 billion metric tons, 3.3% of global emissions.31

27 In the preamble to the proposed rule, EPA said, “… vocational vehicles consist of a wide variety of vehicle types.
Some of the primary applications for vehicles in this segment include delivery, refuse, utility, dump, and cement trucks;
transit, shuttle, and school buses; emergency vehicles, motor homes, tow trucks, among others. These vehicles and their
engines contribute approximately 20 percent of today’s heavy-duty truck sector GHG emissions.” EPA and NHTSA,
“Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium and Heavy-Duty Engines and
Vehicles,” 76 Federal Register 57120, September 15, 2011.
28 “EPA and NHTSA Adopt First-Ever Program to Reduce Greenhouse Gas Emissions and Improve Fuel Efficiency of
Medium- and Heavy-Duty Engines and Vehicles,” August 2011, p. 6, at http://www.epa.gov/otaq/climate/documents/
420f11031.pdf.
29 Ibid., pp. 5-6.
30 “EPA and NHTSA Propose First-Ever Program to Reduce Greenhouse Gas Emissions and Improve Fuel Efficiency
of Medium- and Heavy-Duty Vehicles: Regulatory Announcement,” October 2010, p. 4, at http://www.epa.gov/otaq/
climate/regulations/420f10901.pdf.
31 International Maritime Organization, Updated Study on Greenhouse Gas Emissions from Ships, Executive Summary
(continued...)
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

At these levels, only five countries (the United States, China, Russia, India, and Japan)
individually account for a higher percentage of the world total of CO2 emissions.32
In addition to the CO2 emissions, the low-quality bunker fuel that ships use and the absence of
pollution controls result in significant emissions of black carbon and nitrogen oxides, which also
contribute to climate change. Refrigerants used on ships (hydrofluorcarbons and
perfluorocarbons—HFCs and PFCs) are also potent greenhouse gases when released to the
atmosphere. Thus, the total impact of ships on climate is likely greater than the 3.3% estimate
above.
The authority to control pollution from ships is found in Section 213(a)(4) of the CAA, which
provides general authority to the Administrator to promulgate standards for emissions other than
carbon monoxide, oxides of nitrogen, and volatile organic compounds from “nonroad engines and
vehicles.”33 Fuels are regulated separately under Section 211 of the act.
The language of Section 213 is similar to that for new motor vehicles in Section 202, except that
in place of the words “cause, or contribute,” Section 213 uses the phrase “significantly
contribute”: if the Administrator determines that emissions of GHGs from ships significantly
contribute to air pollution which may reasonably be anticipated to endanger public health or
welfare, she may promulgate such regulations as she deems “appropriate.” Except for the specific
conventional pollutants mentioned in Section 213(a)(2), there is no level of stringency (such as
best available control technology) specified for prospective regulations. The Administrator may
establish classes or categories of ships for the purposes of regulation. There is no deadline for the
promulgation of standards, and in setting them, the Administrator may take into account costs,
noise, safety, and energy factors associated with the application of technology.
A wide variety of measures might be undertaken to reduce emissions from shipping, from simple
operational measures, such as reducing speed or using cleaner fuels, to various hull and propeller
design features that would increase fuel economy. Reducing speed can save substantial amounts
of fuel. A.P. Moller-Maersk, which operates the world’s largest fleet of containerships, reported
that it reduced its CO2 “footprint” per container shipped 15.6% between 2007 and 2011.34
According to the company, “reducing speed 5-10% does increase the number of days at sea, but
reduces both fuel consumption and CO2 emission by more than 15%.”35 The petitions to EPA also
mention improved fleet deployment planning, use of shore-side power while in port, heat
recovery systems, the use of sails as supplemental propulsion sources, and NOx controls, such as
selective catalytic reduction (SCR) or exhaust gas recirculation, as potential emission control
measures.

(...continued)
of Phase 1 Report, 1st September 2008, p. 5 at egserver.unfccc.int/seors/attachment/file_storage/6ep77qqvcujba7k.doc.
Both estimates exclude emissions from naval vessels.
32 Oceana, Shipping Impacts on Climate: A Source with Solutions, p. 2, at http://www.oceana.org/fileadmin/oceana/
uploads/Climate_Change/Oceana_Shipping_Report.pdf.
33 CO, NOx, and VOCs are regulated under §213(a)(3), which requires the imposition of best available control
technology, and set a deadline for such regulation.
34 Maersk Line, Route 2, Sustainability Progress Report, 2011, p. 16, at http://maersklineroute2.com/pdf/
Maersk%20Line%20-%20Sustainability%20Progress%20Report%202011.pdf.
35 See Preparing for the Future, The A.P. Moller – Maersk Group’s Health, Safety, Security and Environment Report
2008, pp. 28-30, at http://media.maersk.com/da/PressReleases/2009/Documents/Maersk%20HSSE%202008_Final.pdf.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

A complicating factor in the regulation of emissions from ocean-going vessels would be that, for
the most part, their GHG emissions occur in international waters, and the sources (the ships) are
not registered in the United States: according to California’s petition, 95% of the fleet calling on
U.S. ports is foreign-flagged. The petitioners assert that these factors are not a bar to EPA
regulation, however, citing as precedent a Supreme Court case that held that the Americans with
Disabilities Act could be applied to foreign-flagged cruise ships so long as the ADA-required
accommodations did not interfere with the ships’ internal affairs or require major, permanent
modifications to the ships.36
In addition to petitioning for regulation of emissions from ships, the petitions from California and
from Oceana et al. stated that EPA should regulate the composition of marine shipping vessel fuel
to control global-climate-change-related emissions, or should require use of marine diesel fuel oil
instead of bunker fuel. The purpose would be to limit the sulfur content of marine fuels and
reduce NOx emissions. We discuss EPA’s authority to regulate fuels in a separate section below,
but note here that EPA, the state of California, and the International Maritime Organization are all
moving forward with regulations to limit the sulfur content of bunker fuel for the purpose of
reducing conventional pollutants. California’s low sulfur fuel requirements went into effect July
1, 2009. In addition, on March 26, 2010, the International Maritime Organization (IMO)
approved an EPA proposal that the entire U.S. coastline except portions of Alaska be designated
as an Emission Control Area, subject to lower sulfur limits in bunker fuel. On July 15, 2011, the
IMO officially added the waters around Puerto Rico and the U.S. Virgin Islands as Emission
Control Areas.37
Sulfur emissions form fine particles of sulfate in the atmosphere, with significant impacts on
public health and welfare. (For a further discussion of these impacts, see CRS Report RL34548,
Air Pollution and Greenhouse Gas Emissions from Ships.) Although harmful as a conventional
pollutant, sulfur emissions are thought by most experts to be beneficial or at least neutral in the
climate context. Sulfates have a cooling effect on the atmosphere, since the particles tend to
reflect solar radiation back into space rather than absorbing it. On the other hand, removing sulfur
might be necessary to prevent the fouling of pollution control equipment that reduces other
pollutants that do lead to warming.
Other Nonroad Engines
Section 213 can also be used to regulate other nonroad vehicles and engines. A similar
endangerment finding would first be required, following which the Administrator may
promulgate such regulations as she deems appropriate to control emissions from the classes or
categories of nonroad engines that she determines “significantly contribute” to the air pollution

36 Spector v. Norwegian Cruiseline, 545 U.S. 119 (2005). In addition, according to the California petition, the United
States can and does enforce pollution standards on ships in its territorial waters, “as can be seen by the fact that the
National Park Service has imposed air pollutant emissions controls on cruise ships, including foreign-flagged cruise
ships (the vast majority of such ships are foreign-flagged), that sail off the coast from Glacier Bay National Park, in
Alaska.” See People of the State of California Acting by and Through Attorney General Edmund G. Brown, Jr.,
“Petition for Rule Making Seeking the Regulation of Greenhouse Gas Emissions from Ocean-Going Vessels,” October
3, 2007, p. 13. The cited regulations are at 36 CFR 13.65(b)(4). The Federal Register citation is 61 Federal Register
27008, 27011 (May 30, 1996).
37 For information on the Emission Control Areas, see the EPA “Ocean Vessels and Large Ships” web page, at
http://www.epa.gov/oms/oceanvessels.htm#emissioncontrol.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

that endangers public health or welfare. The Administrator is to take into account costs, noise,
safety, and energy factors in setting standards. There is no deadline for setting standards.
The nonroad sector is a broad category that includes construction equipment, farm equipment,
forklifts, outdoor power equipment, lawn and garden equipment, and recreational vehicles. This
group accounted for 199.7 million metric tons of CO2 emissions in 2007, according to the two
petitions requesting regulation (see Table 3), 3.3% of total U.S. emissions of CO2 in that year.
According to the ICTA petition, GHG emissions from the nonroad sector increased 49% between
1990 and 2005, a higher rate of emissions increase over the same period than for on-road vehicles
(32%), aircraft (3%), boats and ships (36%), and rail (32%).38
Table 3. Nonroad Sector CO2 Emissions, 2007, by Source Category
(million metric tons)
Category CO2 Emissions
Percent of Nonroad Total
Construction and Mining
63.9 32.0%
Equipment
Agricultural Equipment
39.6
19.8%
Industrial Equipment
27.8
13.9%
Lawn and Garden Equipment
23.8
11.9%
Commercial Equipment
16.4
8.2%
Pleasure Craft
15.8
7.9%
Recreational Equipment
9.4
4.7%
Logging Equipment
1.9
1.0%
Airport Equipment
1.0
0.5%
Railroad Equipment
0.2
0.1%
Total 199.7

Source: ICTA et al., Petition for Rulemaking Seeking the Regulation of Greenhouse Gas Emissions from Nonroad
Vehicles and Engines. According to the petition, the emissions data were compiled by the Western Environmental
Law Center using EPA’s nonroad emissions model.
Given their smaller impact on overall emission levels, EPA has been slower to regulate
conventional (criteria) pollutants from nonroad engines than from motor vehicles. Many of these
engines had few emission control requirements for as many as 25 years after the regulation of
automobiles. In the last decade, however, often following the lead of California, EPA has
promulgated standards for many nonroad categories. Some of these standards, particularly for
diesel-powered equipment and for lawn and garden equipment, have been technology-forcing.
Others, such as for snowmobiles, have been less so.
In general, given the wide variety of engine types and sizes and the configurations of the
equipment itself, the agency has based its standards on a review of individual subcategories and
the technologies available to reduce emissions from specific types of machinery or equipment,

38 International Center for Technology Assessment et al., “Petition for Rulemaking Seeking the Regulation of
Greenhouse Gas Emissions from Nonroad Vehicles and Engines,” January 29, 2008, p. 5.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

rather than applying one across the board standard. Presumably, any GHG standards for this
sector would take the same approach.
Locomotives
On September 21, 2010, EPA received a petition from three environmental organizations to
regulate GHG emissions and black carbon from locomotives. In 2008, locomotives emitted 50.6
million metric tons of greenhouse gases. Although this is less than 1% of total U.S. GHG
emissions, GHG emissions from railroads increased by 30% between 1990 and 2008, more than
twice the rate of increase for total U.S. emissions. In addition, locomotives emit substantial
amounts of black carbon (i.e., soot), which is thought to have significant global warming potential
through its ability to absorb solar radiation and to reduce the reflectivity of snow and ice.
According to a report from NASA’s Goddard Institute for Space Studies cited in the locomotive
petition, “… black soot may be responsible for 25 percent of observed global warming over the
past century.”39 As a result, in addition to requesting that EPA set GHG emission standards for
locomotives, the petition asks EPA to set standards for locomotives’ black carbon emissions.
The CAA requires EPA to set emission standards for new locomotives (and new engines used in
locomotives) in Section 213(a)(5). Unlike almost every other CAA section dealing with mobile
sources, the locomotive subsection does not require an endangerment finding for the
Administrator to act. Instead, it requires the Administrator to set standards that achieve the
greatest degree of emission reduction achievable through the application of technology which she
determines will be available, giving appropriate consideration to cost, noise, energy, and safety
factors.
As it did with the medium- and heavy-duty truck category, EPA discussed several potential
strategies for reducing GHG emissions from locomotives in its July 2008 Advance Notice of
Proposed Rulemaking (ANPR).40 The ANPR identified more than 20 strategies for reducing
emissions from rail transport, including idle reduction equipment, auxiliary power units, hybrid
engines, regenerative braking, and reduction of refrigerant leaks from railcars.
Aircraft
EPA has also received petitions to regulate GHG emissions from aircraft and aircraft engines. In
the United States, aircraft of all kinds are estimated to emit between 2.4% and 3.4% of the
nation’s total greenhouse gas emissions.41 When other factors are considered, the impact of U.S.
aviation on climate change is perhaps twice that size. These factors include the contribution of
aircraft emissions to ozone formation, the water vapor and soot that aircraft emit, and the high
altitude location of the bulk of aircraft emissions. (For additional information on aircraft GHG
emissions, see CRS Report R40090, Aviation and Climate Change.)

39 U.S. National Aeronautics and Space Administration, Goddard Institute for Space Studies, “Black Soot and Snow: A
Warmer Combination,” December 22, 2003, at http://www.gcrio.org/OnLnDoc/pdf/black_soot.pdf.
40 U.S. EPA, “Regulating Greenhouse Gas Emissions Under the Clean Air Act,” Advance Notice of Proposed
Rulemaking, July 30, 2008, 73 Federal Register 44463-44464.
41 The lower percentage includes CO2 emissions from consumption of fuel by military aircraft, general aviation, and
domestic operation of commercial aircraft. The higher estimate includes CO2 emissions from international air travel
originating in the United States, as well.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Two December 2007 petitions requested that EPA address aircraft GHG emissions. Specifically,
the petitions asked that EPA make a finding that aircraft GHG emissions endanger public health
or welfare, and that the agency adopt regulations that allow a range of compliance approaches:
these might include emission limits, operational practices, fees, a cap-and-trade system,
minimizing engine idling time, employing single engine taxiing, or use of ground-side electricity
measures to replace the use of fuel-burning auxiliary power units at airport gates.42
EPA has authority to regulate emissions from aircraft under Section 231 of the CAA. The
language is similar to that for other mobile sources. It requires the Administrator to issue
standards for the emission of any air pollutant from any class or classes of aircraft engines which,
in her judgment, causes or contributes to air pollution which may reasonably be anticipated to
endanger public health or welfare. The regulations are to take effect “after such period as the
Administrator finds necessary ... to permit the development and application of the requisite
technology, giving appropriate consideration to the cost of compliance.” But compared to other
mobile sources, EPA’s CAA authority vis-à-vis aircraft and aircraft engines contains an important
difference: the Administrator must consult with the Administrator of the Federal Aviation
Administration and the Secretary of Transportation in developing emission standards, and is not
allowed to impose new standards if doing so would significantly increase noise and adversely
affect safety. The President may also disapprove any such standards if the Secretary of
Transportation finds that they would create a hazard to aircraft safety.
Unlike ships, aircraft operating in the United States are generally registered here: EPA has cited
data that foreign carriers accounted for only 3% of major carrier operations in the United States in
1999.43 Thus, whether GHG regulations could be applied to foreign flag carriers might seem to
pose less of an issue, at least in terms of whether any potential regulations would address the bulk
of the sector’s U.S. emissions. On the other hand, international air travel is extremely
competitive, and issues of whether regulations can be imposed on foreign carriers have already
been raised in the context of the European Union’s adoption of cap-and-trade requirements for
international aviation as part of the EU Emissions Trading Scheme (EU-ETS).44 U.S. airlines
generally maintain that the imposition of requirements on foreign-flag airlines (i.e., themselves, in
the European Union) violates international trade agreements. Their preference is that any controls
be negotiated through the International Civil Aviation Organization (ICAO) and be applied
equally to all carriers.
In December 2011 the European Court of Justice upheld the EU program, which was slated to
begin in 2012. In response Congress passed, and President Obama signed, P.L. 112-200, which
allows the Secretary of Transportation to prohibit U.S. carriers from participating in the EU-ETS
if the prohibition is “in the public interest.” In December 2012, to allow time for ICAO to

42 For a brief discussion of the petitions, see 73 Federal Register 44460, July 30, 2008. Some of these measures, such
as minimizing engine idling time, employing single engine taxiing, and use of ground-side electricity measures to
replace the use of fuel-burning auxiliary power units, are already widely used by the airlines as fuel-saving measures.
43 U.S. EPA, Office of Air and Radiation, Emission Standards and Test Procedures for Aircraft and Aircraft Engines,
Summary and Analysis of Comments, November 2005, p. 10, at http://www.epa.gov/oms/regs/nonroad/aviation/
420r05004.pdf.
44 For more information, see CRS Report R42828, Update on Controlling Greenhouse Gases from International
Aviation, by Jane A. Leggett.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

develop international standards, the EU suspended the requirement on foreign carriers (including
U.S. carriers) for one year.45
EPA has rarely regulated emissions from aircraft without first negotiating international
agreements through ICAO. ICAO’s regulation of conventional pollutants from aircraft, unlike
EPA’s regulation of the same pollutants from motor vehicles, has consistently avoided forcing
technology. The most recent standards for nitrogen oxides, for example, essentially ratified what
the principal aircraft manufacturers had already achieved.46
Besides petitioning EPA for action on aviation emissions, environmental groups have brought suit
in the District Court for the District of Columbia seeking to force EPA to respond to their
petitions on aircraft, marine vessels, and nonroad engines and vehicles.47 On July 5, 2011, the
court found that EPA has a mandatory duty to determine whether aircraft emissions endanger
public health or welfare, and may be sued for unreasonable delay in doing so. In March 2012,
however, the court ruled that plaintiffs had not shown that EPA had unreasonably delayed such a
decision.48
Fuels
Fuel regulation, whether of bunker fuel, gasoline, or any other type of fuel used in motor vehicles,
their engines, or non-road vehicles and engines, is authorized under Section 211 of the CAA.
Section 211 gives the Administrator authority to control or prohibit the manufacture and sale of
any fuel or fuel additive if she concludes that its emission products may endanger public health or
welfare, or if they will impair to a significant degree the performance of emission control devices.
As with the regulation of engines and vehicles themselves, the Administrator is given substantial
leeway in the design and implementation of fuel regulations and there is no deadline for their
promulgation even after an endangerment finding is made.
GHG emissions from fuels have already been targeted for regulation by the state of California.49
On April 15, 2010, California’s Office of Administrative Law approved regulations to implement
the California Low Carbon Fuel Standard, which has been under development since 2007. The
standard’s goal is to reduce GHG emissions from transportation fuels per unit of energy 10% by
2020. The regulations address emissions from the production, transportation, and consumption of
gasoline, diesel fuel, and their alternatives, including biofuels. They envision compliance both
through the use of lower carbon fuels and through the development of more efficient, advanced-
technology vehicles, such as plug-in hybrids, electric vehicles, and hydrogen fuel cells.
As has been the case with motor vehicles, California has often led the way in the development of
cleaner conventional fuels through technology-forcing regulation, with U.S. EPA later adopting
similar standards. Thus, many view the Low Carbon Fuel Standard as the prototype of another

45 European Union, “Stopping the Clock of ETS and Aviation Emissions Following Last Week’s International Civil
Aviation Organisation (ICAO) Council,” press release, December 11, 2012.
46 “EPA Proposal to Bring Certain Aircraft Up to International Engine Standard,” Daily Environment Report,
September 30, 2003.
47 Center for Biological Diversity v. U.S. EPA, 794 F.Supp. 2d 151 (D.D.C. 2011).
48 Center for Biological Diversity v. U.S. EPA, 2012 Westlaw 967662 (D.D.C. March 20, 2012).
49 For more information, see http://www.arb.ca.gov/regact/2009/lcfs09/lcfs09.htm. For additional background, see CRS
Report R40078, A Low Carbon Fuel Standard: State and Federal Legislation and Regulations.
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

possible use of existing CAA authority to regulate greenhouse gas emissions nationally. On July
29, 2009, the Institute for Policy Integrity at NYU Law School petitioned EPA to establish a cap-
and-trade system to limit greenhouse gas emissions from fuels used in motor vehicles, nonroad
vehicles, and aircraft.
Regulation of fuels would be a way for California or U.S. EPA to obtain reductions from existing
vehicles and engines. As noted earlier, the slow turnover of the vehicle fleet means that emission
reductions from new vehicles will only gradually affect emission levels from the fleet as a whole.
By requiring low carbon fuels, California and EPA could obtain GHG reductions from the entire
fleet more quickly.
On the other hand, measuring the carbon content of fuels is more complicated than it may seem,
particularly if one considers the life-cycle emissions, including indirect impacts of production.
EPA has been embroiled in a controversy over this issue already, as it attempted to develop a
methodology for measuring greenhouse gas emissions from biofuels, as required by the Energy
Independence and Security Act of 2007 (P.L. 110-140).50 For regulations implementing this
provision, EPA developed and later modified a methodology to measure the GHG effects of
indirect land-use changes, such as the switching of land from forest to cropland.51
Conclusion
Table 4 summarizes EPA’s existing authorities over mobile source GHG emissions and the
emissions of each of the sectors discussed in this report. Given the Supreme Court’s remand in
Massachusetts v. EPA, the agency has focused its efforts on motor vehicles, which, as Table 4
shows, account for the majority of mobile source GHG emissions.
By issuing endangerment findings similar to the one it issued for motor vehicles, EPA could move
forward to control GHG emissions from other categories of mobile sources and/or their fuels. On
the other hand, having completed the setting of emission standards for passenger cars, light duty
trucks, and medium- and heavy-duty trucks, EPA has addressed the categories responsible for
more than three-fourths of all mobile source GHG emissions. The next largest category, aircraft,
has rarely been the subject of EPA regulation unless the International Civil Aviation Organization
(ICAO) has first agreed on standards. Other mobile source categories are less significant: each
accounts for less than 1% of total U.S. emissions.
Thus, EPA is following up its initial car and truck standards by expanding its focus to stationary
sources. Stationary sources account for nearly 70% of the nation’s GHG emissions; within that
group electric power plants account for about one-third of all U.S. GHG emissions, a higher
percentage of the nation’s total than all mobile sources combined. New and modified power
plants (as well as other major stationary sources) have been subject to permit requirements and
the imposition of Best Available Control Technology for newly constructed facilities since
January 2, 2011, under EPA’s interpretation of Section 165 of the CAA. The agency also expects

50 Section 202 of the act mandates the use of “advanced biofuels”—fuels produced from non-corn feedstocks and with
50% lower lifecycle greenhouse gas emissions than petroleum fuel—starting in 2009. Of the 36 billion gallons of
renewable fuel required in 2022, at least 21 billion gallons must be advanced biofuel.
51 For information, see CRS Report R40460, Calculation of Lifecycle Greenhouse Gas Emissions for the Renewable
Fuel Standard (RFS).
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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

to promulgate New Source Performance Standards for GHG emissions from new and modified
electric power plants in 2013. (For additional discussion, see CRS Report R41212, EPA
Regulation of Greenhouse Gases: Congressional Responses and Options.)
Table 4. Categories of Sources Whose GHG Emissions Can Be Regulated
Under Title II of the Clean Air Act
(assuming an endangerment finding for the category)
Estimated 2007
GHG Emissions
Percent of Total
CAA Authority
(million tons
U.S. GHG
Category
(Section #)
CO2-equivalent)
Emissions
Passenger Cars
202
671.6
9.4%
Light Duty Trucks
202
569.9
8.0%
Medium- and
202 425.2 5.9%
Heavy-Duty
Trucks
Aircraft (domestic
231 171.8 2.4%
operation)
Construction and
213 63.9
0.9%
Mining Equipment
Ships and Other
213 55.2
0.8%
Boatsa
Locomotives 213
54.3
0.8%
Agricultural
213 39.7
0.6%
Equipment
Industrial
213 27.8
0.4%
Equipment
Lawn and Garden
213 23.8
0.3%
Equipment
Commercial
213 16.4
0.2%
Equipment
Pleasure Craft
213
15.8
0.2%
Buses 202
12.5
0.2%
Recreational
213 9.4
0.1%
Equipment
Motorcycles 202
2.1 <0.1%
Logging Equipment
213
1.9
<0.1%
Airport Equipment
213
1.0
<0.1%
Railroad
213 0.2
<0.1%
Equipment
Totala
2,162.5
30.2%
Source: U.S. EPA and ICTA.
a. Does not include international bunker fuel.

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Cars, Trucks, and Climate: EPA Regulation of Greenhouse Gases from Mobile Sources

Author Contact Information

James E. McCarthy
Brent D. Yacobucci
Specialist in Environmental Policy
Section Research Manager
jmccarthy@crs.loc.gov, 7-7225
byacobucci@crs.loc.gov, 7-9662


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