I-L.
Average Annual Emissions and Fuel
Consumption for Gasoline-Fueled
Passenger Cars and Light Trucks
The amount of pollution that a vehicle emits and the rate at which
it consumes fuel are dependent on many factors. The U.S.
Environmental Protection Agency (EPA) has developed a series of
computer models that estimate the average emissions for different
types of highway vehicles. This fact sheet is one of a series on high'
way vehicle emission factors. It presents average annual emissions and
fuel consumption for gasoline-fueled light-duty vehicles (passenger
cars) and light-duty trucks (pickup trucks, sport-utility vehicles, and
the like).
Introduction
There are a number of factors that affect the rate at which any vehicle emits air
pollutants. Some of the most important are:
• vehicle type/size (passenger cars, light-duty trucks, heavy-duty trucks, urban and
school buses, motorcycles)
• vehicle age and accumulated mileage
• fuel used (gasoline, diesel, others)
• ambient weather conditions (temperature, precipitation, wind)
• maintenance condition of the vehicle (well maintained, in need of maintenance,
presence and condition of pollution control equipment)
• how the vehicle is driven (e.g., long cruising at highway speeds, stop-and-go
urban congestion, typical urban mixed driving)
United States
Environmental Protection
Agency
Office of Transportation and Air Quality
EPA420-F-08-024
October 2008
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The most current version of the computer model that EPA uses to estimate average in-use emissions
from highway vehicles is MOBILE6.2. EPA, the States, and others use this model to estimate
total emissions of pollutants generated by highway vehicles in various geographic areas and over
specific time periods. The emission rates or "emission factors" presented in this fact sheet are
based on national average data
representing the in-use fleet as of
July 2008.
The emission rates for hydro-
carbons (both volatile organic
compounds [VOCs] and total
hydrocarbons [THC]), carbon
monoxide (CO), nitrogen oxides
(NOx), and particulate matter
(PM10 and PM25) are presented in
the following tables. The hydro-
carbon (HC) numbers include
both tailpipe and evaporative
emissions, whereas the rates for
the other pollutants are for tail-
pipe emissions only.
The emission rates assume an av-
erage, properly maintained vehi-
cle, operating on typical gasoline
on a warm summer day. Emission
rates can be higher in very hot
weather (especially HC) or very
cold weather (especially CO).
National average values are used
for registration distributions by
age (what fraction of all vehicles
of each specific type, in use today,
are of the current model year,
one to two years old, two to three
years old, and so forth up to 25
years old) and annual mileage
accumulation rates by age (newer
vehicles tend to be driven more
miles per year than do older vehi-
cles). Some of the other primary
assumptions incorporated in these
emission factors are:
Abbreviations and Acronyms Used
CO: Carbon monoxide; a regulated pollutant
CO2: Carbon dioxide; the primary byproduct of
all fossil fuel combustion
FTP: Federal Test Procedure; the primary test
used in certifying vehicle compliance with
emission standards
g: gram(s)
g/mi: grams per mile
GHG: Greenhouse gas or gases, such as CO2,
that accumulate in the atmosphere and
contributes to potential climate change
HC: Hydrocarbons; molecules formed of hydrogen
and carbon that constitute gasoline, diesel,
and other petroleum-based fuels; a
regulated pollutant
Ib: pound
NOx: Nitrogen oxides; a regulated pollutant
PM_ Particulate matter under 10 microns
diameter; a regulated pollutant
PM j, Particulate matter under 2.5 microns
diameter, sometimes referred to as
"fine particulate"
ppm: parts per million
psi: pounds per square inch
RVP: Reid vapor pressure; a standardized meth
od for expressing the volatility, or tenden
cy to evaporate, of gasoline
SUV: Sport-utility vehicle; a subset of all light-
duty trucks; examples include most Daim
ler-Chrysler Jeep models, Ford Escape,
Ford Explorer, GMC Yukon, etc.
THC: Total hydrocarbons
VMT: Vehicle miles traveled
VOC: Volatile organic compounds; equivalent
to THC plus aldehydes minus both
methane and ethane
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• Ambient temperature: 72 to 92 °F day time range
• Nominal gasoline volatility: 9.0 psi RVP
• Weathered fuel volatility: 8.6 psi RVP
• Gasoline sulfur content: 30 ppm
• Average speed: 27.6 miles per hour
• I/M program: No
• Reformulated gasoline: No
These calculations are based on average annual passenger car mileage of 12,000 miles and aver-
age annual light-duty truck mileage of 15,000 miles. Fuel consumption is based on the estimated
average in-use fuel economy: 24.1 miles per gallon (mpg) for passenger cars and 17.3 mpg for
light trucks. These values are also from the MOBILE6.2 model.
These emission factors and fuel consumption rates are for gasoline-fueled passenger cars and
light-duty trucks only. Diesel cars represent less than 0.5 percent of all cars on the road in the
United States as of 2005, and diesel light trucks represent less than 2 percent of all light-duty
trucks on the road. In general, diesel vehicles (relative to gasoline vehicles of similar size and
age) will have lower emissions of HC and CO, and higher emissions of NOx and particulate
matter. Diesel fuel economy tends to be better than that of similar gasoline-fueled vehicles,
meaning total fuel consumption and CO2 emissions per vehicle per year tend to be lower.
Changes from Previous Versions of this Fact Sheet
The emission factors presented below are not directly comparable to those used in previous
versions of this fact sheet due to the extensive changes made to the MOBILE model in order
to better represent real-world driving. In earlier versions, the emission factors were based on
an average travel speed of 19.6 miles per hour (mph). This is the average speed of the Federal
Test Procedure (FTP), which is the basis for certification of new vehicles to applicable emission
standards. The FTP is considered to be reasonably representative of overall traffic in urbanized
areas; it includes stops and starts, idling time, accelerations and decelerations, and short cruising
r \ stretches. However, it does not include any acceleration or deceleration rates greater than 3.4
^^ mph per second (mph/s), nor does it include any travel at speeds greater than 60 mph.
The emission factors produced by MOBILE6.2 are based on national average data on the frac-
tion of total vehicle miles traveled (VMT) accrued on each of four major roadway types, and
national average traffic speeds associated with each of these facility types. The four roadway
types are limited access highways (freeways, expressways), ramps (entrance and exit ramps to
and from limited access highways), arterials (primary surface roadways), and local and collector
^H roads (local streets and minor surface roadways).
c/}
These emission factors account for the fact that a single value of average speed is not adequate
for the characterization of real-world driving patterns. For example, driving patterns associated
with an average speed of 40 mph on a limited access highway are not the same as driving pat-
terns associated with an average speed of 40 mph on an arterial route; in the first case, 40 mph
W implies heavy traffic with some congestion and varying speeds, while in the latter case 40 mph
represents near free-flow conditions. The emission factors developed for the four roadway types
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include much sharper acceleration and deceleration rates (up to 6.9 mph/s), which result in
significantly higher emission rates for short periods of time, and higher maximum speeds (up to
75 mph on limited access highways).
Thus, these emission factors differ from those that would have been estimated using previous
versions of the MOBILE model, which assumed a single driving pattern with an average speed of
19.6 mph, no accelerations or decelerations exceeding 3.4 mph/s, and no driving over 60 mph.
These newer emission factors are much closer to being representative of observed real world
driving patterns and speeds, and thus more accurately represent emissions in use.
Average Emissions and Fuel Consumption for Passenger Cars*
Pollutant/Fuel
voc
THC
CO
NOx
PM10
PM25
C02
Gasoline
Consumption
Emission & Fuel
Consumption Rates
(per mile driven)
1 .034 grams (g)
1.077g
9.400 g
0.693 g
0.0044 g
0.0041 g
368.4 g
0.041 49 gallons (gal)
Calculation
(1 .034 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(1 .077 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(9.400 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(0.693 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(0.0044 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(0.0041 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(368.4 g/mi) x (12,000 mi/yr) x (1 lb/454 g)
(1 2,000 mi/yr)/ (24.1 mi/gal)
Annual
Emission & Fuel
Consumption
27.33 Ib
28.47 Ib
248.46 Ib
18.32lb
0.12 Ib
0.11 Ib
9,737.44 Ib
497.93 gal
*See Endnotes
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Average Emissions and Fuel Consumption for Light-Duty Trucks*
(most pick-uptrucks, SUVs, etc.)
ts
Pollutant/Fuel
voc
THC
CO
NOx
PM10
PM25
C02
Gasoline
Consumption
Emission & Fuel
Consumption Rates
(per mile driven)
1 .224 grams (g)
1.289g
11.84g
0.95g
0.0049 g
0.0045 g
513.5 g
0.05780 gallons (gal)
Calculation
(1.224 g/mi) x (15,000 mi/yr) x (1 lb/454 g)
(1.289 g/mi) x (15,000 mi/yr) x (1 lb/454 g)
(11.84 g/mi) x (15,000 mi/yr) x (1 lb/454 g)
(0.95 g/mi) x (15,000 mi/yr) x (1 lb/454 g)
(0.0049 g/mi)x (15,000 mi/yr) x (1 lb/454 g)
(0.0045 g/mi) x (15,000 mi/yr) x (1 lb/454 g)
(513.5 g/mi) x (15,000 mi/yr) x (1 lb/454 g)
(15,000 mi/yr)/ (17.3 mi/gal)
Annual
Emission & Fuel
Consumption
32.35 Ib
34.07 Ib
312.95 Ib
25.11 Ib
0.13 Ib
0.12 Ib
13, 572.69 Ib
693.64 gal
*See Endnotes
For More Information
The other fact sheets in this series and additional information are available on the Office of
Transportation and Air Quality's Web site at:
Emission factor fact sheets:
Modeling and estimating vehicle emissions:
Fuel economy:
Improving fuel economy and reducing emissions:
Finding the "greenest" vehicle:
www.epa.gov/otaq/consumer.htm
www.epa.gov/otaq/models.htm
www.epa.gov/fueleconomy
www.fueleconomy.gov
www.epa.gov/epahome/trans.htm
www.fueleconomy.gov/feg/drive.shtml
www.epa.gov/greenvehicles
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Endnotes
1. Figures presented above are averages only. Individual vehicles can differ substantially in
terms of both annual miles traveled and pollution emitted per mile from values indicated here.
Values shown may differ slightly from original sources due to rounding.
2. These emission factors and fuel consumption rates are averages for the entire in-use fleet
as of July 2008. Newer vehicles generally emit less pollution and use less gasoline, while older
vehicles generally emit more pollution and use more gasoline. This is due to several factors,
including the increasing stringency of emission standards over time and the deterioration (deg-
radation) in the performance of emission control technology (e.g., catalytic converters) with
increasing age and accumulated mileage.
3. Carbon dioxide (CO2), while not regulated as an air pollutant, is the transportation sector's
primary contribution to climate change. Carbon dioxide emissions are essentially proportional
to fuel consumption (and inversely proportional to fuel economy) - each 1% increase in fuel
consumption results in a corresponding 1% increase in carbon dioxide emissions. About 19.4
Ib CO2 is produced for every gallon of gasoline combusted. Passenger cars and light-duty trucks
also emit small amounts of other greenhouse gases (GHGs); thus, total GHG emissions
from these vehicles are slightly greater than the CO2 emission totals shown in this fact sheet.
4. All of the emission estimates provided in this document are consistent, in terms of assump-
tions made and modeling methodology, with those provided in the other fact sheets in this
series: "Idling Vehicle Emissions" (EPA420-F-08-025), "Average In-Use Emission Factors for
Urban Buses and School Buses" (EPA420-F-08-026), and "Average In-Use Emissions from
Heavy-Duty Trucks" (EPA420-F-08-027).
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