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Office of Transportation EPA420-F-05-021 

and Air Quality June 2005 

Regulatory

Announcement 

Final Rule on In-Use Testing

Program for Heavy-Duty Diesel

Engines and Vehicles 

The U.S. Environmental Protection Agency (EPA) is establishing a 

manufacturer-run, in-use emissions testing program for heavy-duty 

diesel trucks. Under this program, manufacturers will measure gaseous 

and particulate exhaust emissions from diesel engines using portable 

onboard emission measurement systems. This cooperative effort represents a significant advance in helping to ensure that the benefits of more 

stringent emission standards are realized under real-world driving 

conditions. 

Background 

EPA has issued five rules regarding diesel engines since 1999. These include 

the 2004 and 2007 Heavy-Duty Diesel Motor Vehicle Engines Rules, Recreational Marine Diesel Engines Rule, Commercial Marine Diesel Engines Rule, 

and the Clean Air Nonroad Diesel Rule for compression-ignition engines.The 

Engine Manufacturers Association (EMA) and some manufacturers challenged parts of the highway and marine rules regarding legal authority and 

technical feasibility of certain emission standards called the Not-To-Exceed 

Standards (NTE). EPA, the California Air Resources Board (ARB), and 

EMA, along with its member companies, worked cooperatively to reach a 

settlement agreement that included provisions for a manufacturer run, in-use 

emissions testing program. This final rule implements the key elements of that 

agreement. 
The new testing program will assess in-use gaseous emissions (hydrocarbons, 

carbon monoxide, and nitrogen oxides) and particulate matter from the 

exhaust of heavy-duty diesel trucks. For the first time, this will be accomplished using portable emission measurement systems. Previously, engine 

emissions testing involved removing the engine from the truck and testing the 

engine in a laboratory on an engine dynamometer. Starting in the mid-1990s 

EPA facilitated research into portable systems by developing and using 

prototype systems in its compliance programs. Portable systems were placed 

inside of the vehicles to measure emissions performance during real-world 

operating conditions. It became clear that these systems offered advantages 

over conventional approaches to assess in-use exhaust emissions from engines 

for design improvement, research, modeling, and compliance purposes. 

In a largely unprecedented example of proactive government and industry 

cooperation, prior to any formal rulemaking initiative, manufacturers have 

agreed to implement this new type of in-use emission testing program. The 

resulting collaborative program, which advances EPA’s clean diesel program, 

is a significant step forward for both parties in helping ensure that heavy-duty 

diesel engines comply with applicable emission standards throughout their 

useful lives while reducing overall compliance burdens. 

Program Overview 

Under the program, manufacturers will test fleet or customer-owned, in-use 

trucks. Manufacturers will tap into existing customer relationships and create 

new lines of communication with customers, all of which is expected to fortify 

the engine development process. This will enhance the manufacturer’s ability 

to catch any problem engines early on, and encourage future engine designs 

that are cleaner and more durable. 

Manufacturers will monitor compliance by testing in-use diesel engines during 

normal vehicle operation. If noncomplying engines are identified, the manufacturer will test more engines for the purpose of determining if any further 

action is necessary. EPA will likewise use the in-use data to make independent evaluations about the possible need to pursue further actions. The in-use 

test data, which have never been collected on this large a scale, will be used 

by EPA to assure that emission standards are being met, and by manufacturers to improve their engine designs. The data will also be available to the 

public. 

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Key Elements 

• Fully enforceable program beginning in the 2007 model year for gaseous 

emissions, when new NTE and tailpipe emission standards for nitrogen 

oxides (NOx) and particulate matter (PM) take effect. 

• Pilot program for gaseous emissions for 2005 and 2006 model years 

EPA and the manufacturers to gain the necessary experience with in-use 

testing protocols and generation of in-use test data using portable 

emission measurement systems. 

• Enforceable and pilot programs for PM begin one year after the gaseous 

programs begin. 

• Monitors in-use emissions of diesel vehicles with portable emission 

measurement systems. Pollutants to be measured: Hydrocarbons (HC), 

Carbon Monoxide (CO), NOx and PM. 

• Testing will be conducted on in-use vehicles, under real-world driving 

conditions, within the engine’s useful life to monitor for NTE compliance 

and to help ensure overall compliance with the emission standards. 

• Measurement "accuracy"margins established to account for the emissions 

measurement variability associated wiht these usnits in the field. 

o During the pilot program years, manufacturers will use interim 

margins based on current experience with portable and laboratory 

measurement systems. 

o Accuracy margins for the fully enforceable program are being 

developed through a joint EPA-industry research program. 

• Testing conducted and paid for by manufacturers with EPA oversight. 

• Addresses a serious, long-standing need for “real-world” in-use testing 

data. 

• The California Air Resources Board intends to adopt a parallel in-use 

testing program. 

• A nonroad diesel engine in-use testing program patterned after the

heavy-duty truck program is expected in the 2010 time frame.

Economic, Health and Environmental Impacts 

EPA expects that 13 heavy-duty diesel engine manufacturers will be involved 

in the program. Total annual costs are estimated at about $1.7 million. 

This in-use emissions testing program is expected to help ensure that the 

intended health and environmental benefits from recently-adopted emission 

regulations are realized throughout the entire useful lives of heavy-duty diesel 

engines. 

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For More Information 

You can access documents on this final rule on EPA’s Office of Transportation 

and Air Quality Web site at: 

www.epa.gov/otaq/hd-hwy.htm 

For further information, please contact Rich Wilcox at: 

U.S. Environmental Protection Agency

Office of Transportation and Air Quality

2000 Traverwood Drive

Ann Arbor, MI 48105

734-214-4390

E-mail: wilcox.rich@epa.gov

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