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Emission

Facts

 Printed on Recycled Paper

United States

Environmental Protection

Agency

Air and Radiation EPA420-F-03-002

February 2003

Office of Transportation and Air Quality

Impacts of Truck Idling on Air

Emissions and Fuel Consumption

In the United States, heavy-duty diesel truck idling contributes

significantly to both energy consumption and air emissions. EPA

estimates that idling trucks consume, annually, over 950 million gallons

of diesel fuel, and emit over 10 million tons of carbon dioxide (CO2) and

approximately 200,000 tons of oxides of nitrogen (NOx). This fact sheet

summarizes the results of EPA’s comprehensive truck idling test

program. The full report is available at the following web address:

www.epa.gov/otaq/retrofit/idling.htm.

Idling Test Program

EPA’s truck idling test program was conducted over a two year period at

the U.S. Army’s Aberdeen Test Center in Aberdeen, Maryland. EPA

developed an idling test program that was reviewed by the American

Trucking Association and the 21st Century Truck Partnership (government-industry group consisting of major U.S. truck and engine manufacturers).

To test actual long duration idling conditions, we

selected representative truck idling scenarios that

included the following categories:

• truck selection

• temperature ranges

• engine speed (rpm) ranges

• accessory loads

Average Truck Idling

Emissions & Fuel Use

• 140 g/hr of NOx

• 8200 g/hr of CO2

• 0.80 gal/hr of diesel fuel
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Nine heavy-duty diesel trucks were selected for testing, from model years

1985-2001; thus representing the trucks traveling the roads today. The

trucks/engines were manufactured by leading U.S. companies, including

Caterpillar, Cummins, Detroit Diesel, Ford, Freightliner, International,

Kenworth, and Volvo.

The trucks were tested in a climate controlled chamber, at 0o

 F, 65o F, and

90o F. This temperature range accounts for idling not only in weather

extremes, but in moderate conditions as well.

Since truck drivers can adjust the engine speed (rpms) to provide more

power at idle, the test program included engine tests from 600-1200 rpm.

Use of the air conditioning or heat would normally require higher engine

rpms, usually above 1000 rpm. Since not all idling takes place during air

conditioner/heat needs, we also tested at the lower 600 rpm.

Since truck drivers idle for different reasons, the test program tested

trucks under the following loads: air conditioning operating, heat operating, and no accessories operating. The first truck was tested for six hours

to determine the emissions steady state, that is, the point upon which the

emissions remained the same. We determined that this point was three

hours. Therefore, all subsequent tests were for three hours per truck.

Results

After 42 unique test scenarios that represent actual long-duration truck

idling conditions, the test program concluded that, on average, a typical

1980s-2001 model year idling truck emits 140 grams per hour (g/hr) of

NOx and 8200 g/hr of C02 and consumes about 0.80 gallons per hour of

diesel fuel.

For More Information

You can access the full report, "Study of Exhaust Emissions from Idling

Heavy-Duty Diesel Trucks and Commercially Available Idle-Reducing

Devices" (EPA420-R-02-025, October 2002), at:

www.epa.gov/otaq/retrofit/idling.htm

You can also contact the OTAQ library for document information at:

U.S. Environmental Protection Agency

2000 Traverwood Dr.

Ann Arbor, MI 48105

(734) 214-4311

E-mail: Group AALibrary@epa.gov

Truck

Selection

Temperature

Ranges

Engine

Speed

Accessory

Loads