Emission Facts
 

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 emissions for different types of highway vehicles. This fact sheet is one of 

a series on highway vehicle emission factors. It presents average emission rates for gasoline-fueled and diesel heavy-duty vehicles. 

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 vehicles 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. 

Office of Transportation and Air Quality 

EPA420-F-08-027 

October 2008 
 

 

 

 

 

 

 

 

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 (PM and PM ) are presented in the following tables. The hydrocarbon 10 2.5

numbers include both tailpipe and evaporative emissions, whereas the rates for the other pollutants 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 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) 

•	 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 associated with an average speed 

of 40 miles per hour (mph) on 

a limited access highway are 

not the same as driving patterns 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: 

g/bhp-hr: 

g/mi: 

GVW: 

HC: 

HDDV: 

HDGV: 

NOx: 

PM10: 

PM2.5: 

ppm: 

psi: 

RVP: 

THC: 

VMT: 

VOC: 

Carbon monoxide; a regulated pollutant 

grams per brake horsepower-hour; the unit 

used in establishing emission standards and 

measuring emissions from heavy-duty engines 

grams per mile; a standard form of expressing 

highway vehicle emission rates 

Gross vehicle weight 

Hydrocarbons; molecules formed of hydrogen 

and carbon that constitute gasoline, diesel, 

and other petroleum-based fuels; a regulated 

pollutant 

Heavy-duty diesel vehicle 

Heavy-duty gasoline-fueled vehicle 

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” 

parts per million 

pounds per square inch 

Reid vapor pressure; a standardized method 

for expressing the volatility, or tendency to 

evaporate, of gasoline 

Total hydrocarbons including methane 

Vehicle miles traveled 

Volatile Organic Compounds; equivalent to 

THC plus aldehydes minus both methane and 

ethane

Emission Facts
 

2 
 

 

 

 

 

 

 

Emission Facts
 

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 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 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 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 installed 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 lb gross vehicle weight and are equipped with heavy-duty engines, a distinct 

category under EPA’s highway vehicle pollution control regulations. The heaviest trucks (heavyduty diesel trucks in GVW classes VIIIa and VIIIb) 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. 


 
 

Table 1: Average In-Use Emission Rates for Heavy-Duty Vehicles* 

(in grams per mile) 

Pollutant 

VOC
 

THC
 

CO
 

NOx
 

PM2.5
 

PM10
 

* See Endnotes 

HDGV HDDV 

(gasoline) (diesel) 

1.586 0.447 

1.635 0.453 

13.130 2.311 

2.914 8.613 

0.044 0.202 

0.051 0.219

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) 

IIb: 8,501-10,000 lb (e.g., full-size pick-up trucks, very large passenger vans) 

III: 10,001-14,000 lb (e.g., panel trucks, small enclosed delivery trucks) 

IV: 14,001-16,000 lb (e.g., city delivery trucks, rental trucks) 

V: 16,001-19,500 lb (e.g., bucket utility trucks, large walk-in delivery trucks) 

VI: 19,501-26,000 lb (e.g., rack trucks, single axle vans) 

VII:	 26,001-33,000 lb (e.g., tow truck, garbage collection trucks) 

VIIIa: 33,001-60,000 lb (e.g., long-haul semi-tractor trailer rigs)
 

VIIIb: > 60,000 lb (e.g., double long-haul semi-tractor trailer rigs)

Emission Facts
 

4 
 

 

Table 2: Average Heavy-Duty Truck Emission Rates by GVW Class* 

(in grams per mile) 

Pollutant Fuel IIb III IV V VI VII 

VOC gas 

diesel 

1.353 

0.189 

1.667 

0.201 

4.234 

0.262 

2.632 

0.274 

2.477 

0.365 

2.857 

0.453 

gas 1.400 1.713 4.319 2.693 2.535 2.920 

diesel 0.194 0.204 0.266 0.278 0.370 0.459 

CO gas 

diesel 

11.220 

0.839 

15.810 

0.908 

33.860 

1.163 

19.580 

1.189 

18.130 

1.367 

23.130 

1.719 

NOx gas 

diesel 

2.734 

3.088 

2.920 

3.298 

4.133 

4.352 

3.735 

4.548 

3.650 

5.990 

4.199 

7.471 

PM2.5 gas 

diesel 

0.043 

0.091 

0.045 

0.073 

0.058 

0.089 

0.046 

0.079 

0.045 

0.172 

0.046 

0.177 

PM10 gas 

diesel 

0.049 

0.099 

0.051 

0.079 

0.074 

0.096 

0.055 

0.085 

0.054 

0.186 

0.056 

0.192 

(1) There are no gasoline-fueled heavy trucks in this weight category. 

* See Endnotes 

For More Information 

VIIIa VIIIb 

3.628 (1) 

0.455 0.545 

3.704 (1) 

0.461 0.552 

28.560 (1) 

2.395 3.109 

4.892 (1) 

9.191 10.990 

0.049 (1) 

0.215 0.238 

0.061 (1) 

0.233 0.259 

Emission Facts
 

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: www.epa.gov/otaq/consumer.htm 

Modeling and estimating vehicle emissions: 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 substantially 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 


 
Emission Facts
 

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).