Average In-Use Emissions from
Heavy-Duty Trucks
The amount of pollution that a vehicle emits is dependent on many
factors. The U.S. Environmental Protection Agency (EPA) has
developed a series of computer models that estimate the average emis-
sions for different types of highway vehicles. This fact sheet is one of
a series on highway vehicle emission factors. It presents average emis-
sion rates for gasoline-fueled and diesel heavy-duty vehicles.
I-L.
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)
• type of driving (e.g., long cruising at highway speeds, stop-and-go urban
congestion, typical urban mixed driving)
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 ve-
hicles in various geographic areas and over specific time periods. The emission rates (or
"emission factors") presented for gasoline-fueled and diesel heavy-duty trucks in this
fact sheet are based on national average data representing the in-use fleet as of July
2008. These estimates are suitable for use in obtaining first-order approximations of
vehicle emissions.
United States
Environmental Protection
Agency
Office of Transportation and Air Quality
EPA420-F-08-027
October 2008
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The emission rates (or "emission factors") for hydrocarbons (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 hydrocarbon
numbers include both tailpipe and evaporative emissions, whereas the rates for the other pollut-
ants are for tailpipe emissions only.
The emission rates assume an average, properly maintained heavy-duty truck operating on
typical gasoline or diesel fuel on a warm summer day. Emission rates can be higher in very hot
weather (especially HC) or very
cold weather (especially CO),
The emission factors produced
by MOBILE6.2 are based on
the fraction of total vehicle
miles traveled (VMT) accrued
on each of four major roadway
types, and national average traf-
fic 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)
• local and collector roads
(local streets and minor
surface roadways)
These emission rates 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 as-
sociated with an average speed
of 40 miles per hour (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
implies heavy traffic with some
Abbreviations and Acronyms Used
CO: Carbon monoxide; a regulated pollutant
g/bhp-hr: grams per brake horsepower-hour; the unit
used in establishing emission standards and
measuring emissions from heavy-duty engines
g/mi: grams per mile; a standard form of expressing
highway vehicle emission rates
GVW: Gross vehicle weight
HC: Hydrocarbons; molecules formed of hydrogen
and carbon that constitute gasoline, diesel,
and other petroleum-based fuels; a regulated
pollutant
HDDV: Heavy-duty diesel vehicle
HDGV: Heavy-duty gasoline-fueled vehicle
NOx: Nitrogen oxides; a regulated pollutant
Particulate matter under 10 microns diameter; a
regulated pollutant
Particulate matter under 2.5 microns diameter,
sometimes referred to "fine particulate"
ppm: parts per million
psi: pounds per square inch
RVP: Reid vapor pressure; a standardized method
for expressing the volatility, or tendency to
evaporate, of gasoline
THC: Total hydrocarbons including methane
VMT: Vehicle miles traveled
VOC: Volatile Organic Compounds; equivalent to
THC plus aldehydes minus both methane and
ethane
PM
2.5
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congestion and varying speeds, while in the latter case 40 mph represents near free-flow condi'
tions. The emission factors developed for the four roadway types include hard acceleration and
deceleration rates (up to 6.9 mph/second), which result in significantly higher emission rates for
short periods of time, and maximum speeds up to 75 mph for parts of the limited access highway
driving patterns.
National average values are used for registration distributions by age (what fraction of all ve-
hicles 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 vehicles) and by gross
vehicle weight (GVW) class. Some of the other primary assumptions made in developing these
emission factors are:
• 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
• Diesel fuel sulfur content: 11 ppm
• I/M program: No
• Reformulated gasoline: No
To estimate in-use emission rates from heavy-duty trucks, the emission rates from heavy-duty
engines, expressed and regulated in terms of grams per brake horsepower-hour (g/bhp-hr), must
be converted to units of grams per mile (g/mi). Heavy-duty engines emission standards are stated
in g/bhp-hr to account for the fact that the same engines may be used in a wide range of final
vehicle applications. The work performed by a heavy-duty engine installed in a truck of GVW
Class III, for example, is much less than the work that engine would be required to do if in-
stalled in a truck of GVW Class VII.
This conversion, from mass pollutant emitted per unit work to mass pollutant emitted per unit
distance traveled, is performed in MOBILE6.2 through the use of "conversion factors" that
express the average amount of work required to move a given heavy-duty truck over one mile
(brake horsepower-hour per mile, or bhp-hr/mi).
Average In-use Emission Rates for Heavy-Duty Trucks
Table 1 presents emission rates for gasoline-fueled and diesel-powered heavy-duty trucks that
are averages for the entire in-use fleet as of July 2008. Heavy-duty trucks are vehicles that are
greater than 8,500 Ib gross vehicle weight and are equipped with heavy-duty engines, a distinct
category under EPA's highway vehicle pollution control regulations. The heaviest trucks (heavy-
duty diesel trucks in GVW classes Villa and VHIb) are used mostly for the interstate transport
of goods, and in some cases accumulate more than 250,000 miles annually. Those trucks at
the lighter end of the heavy-duty vehicle category (gasoline-fueled and diesel trucks in GVW
Classes III-V) are used more in short-haul applications, and generally average under 30,000
miles annually. The overall average emission factors presented for each category are weighted to
account for the distribution of vehicles across the different weight classes.
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Table 1: Average In-Use Emission Rates for Heavy-Duty Vehicles*
(in grams per mile)
Pollutant
voc
THC
CO
NOx
PM9,
PMin
HDGV
(gasoline)
1.586
1.635
13.130
2.914
0.044
0.051
HDDV
(diesel)
0.447
0.453
2.311
8.613
0.202
0.219
See Endnotes
Table 2 presents average in-use emission rates for heavy-duty gasoline trucks and heavy-duty
diesel trucks, separated by various weight classes. The GVW weight classes are:
Heavy-Duty Vehicle Classifications
(Gross Vehicle Weight Rating)
lib: 8,501-10,000 Ib (e.g., full-size pick-up trucks, very large passenger vans)
III: 10,001-14,000 Ib (e.g., panel trucks, small enclosed delivery trucks)
IV: 14,001-16,000 Ib (e.g., city delivery trucks, rental trucks)
V: 16,001-19,500 Ib (e.g., bucket utility trucks, large walk-in delivery trucks)
VI: 19,501-26,000 Ib (e.g., rack trucks, single axle vans)
VII: 26,001-33,000 Ib (e.g., tow truck, garbage collection trucks)
Villa: 33,001-60,000 Ib (e.g., long-haul semi-tractor trailer rigs)
VHIb: > 60,000 Ib (e.g., double long-haul semi-tractor trailer rigs)
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Table 2: Average Heavy-Duty Truck Emission Rates by GVW Class*
(in grams per mile)
Pollutant
voc
CO
NOx
PM2.5
PM10
Fuel
gas
diesel
gas
diesel
gas
diesel
gas
diesel
gas
diesel
gas
diesel
lib
1.353
0.189
1.400
0.194
11.220
0.839
2.734
3.088
0.043
0.091
0.049
0.099
III
1.667
0.201
1.713
0.204
15.810
0.908
2.920
3.298
0.045
0.073
0.051
0.079
IV
4.234
0.262
4.319
0.266
33.860
1.163
4.133
4.352
0.058
0.089
0.074
0.096
V
2.632
0.274
2.693
0.278
19.580
1.189
3.735
4.548
0.046
0.079
0.055
0.085
VI
2.477
0.365
2.535
0.370
18.130
1.367
3.650
5.990
0.045
0.172
0.054
0.186
VII
2.857
0.453
2.920
0.459
23.130
1.719
4.199
7.471
0.046
0.177
0.056
0.192
Villa
3.628
0.455
3.704
0.461
28.560
2.395
4.892
9.191
0.049
0.215
0.061
0.233
VHIb
(i)
0.545
(i)
0.552
(i)
3.109
(i)
10.990
(i)
0.238
(i)
0.259
(1) There are no gasoline-fueled heavy trucks in this weight category,
* 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:
www.epa.gov/otaq/consumer.htm
www.epa.gov/otaq/models.htm
Converting heavy-duty engine emission rates to in-use heavy-duty truck emission rates:
www.epa.gov/otaq/models/mobile6/r02006.pdf
www.epa.gov/otaq/models/mobile6/r02005.pdf
Endnotes
1. Figures presented in this document are averages only. Individual trucks may differ substantial-
ly in terms of pollution emitted per mile from values indicated here. Values may differ slightly
from original sources due to rounding,
2. These emission factors are averages for the entire in-use fleet as of July 2008. Newer trucks
generally will have lower emissions, as they are built to comply with more stringent emission
standards and have not yet accumulated high odometer mileages, while older trucks generally
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will have higher emissions, as they were built to comply with more lenient emission standards in
effect for past years and generally have accumulated much higher odometer mileages,
3. All emission estimates provided in this fact sheet are consistent, in terms of assumptions made
and modeling methodology, with those provided in the other fact sheets in this series: "Average
Annual Emissions and Fuel Consumption for Gasoline-Fueled Passenger Cars and Light Trucks"
(EPA420'F-08'024), "Idling Vehicle Emissions" (EPA420'F-08-025), and "Average In-Use
Emission Factors for Urban Buses and School Buses" (EPA420'F-08'026).
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