Jump to main content.

Regulatory Announcement:
Final Rule on In-Use Testing Program for Heavy-Duty Diesel Engines and Vehicles

EPA420-F-05-021, June 2005
Read this Regulatory Announcement in PDF format. (4 pp, 46K , About PDF Files)

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.


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.

top of page

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.

top of page

Key Elements

top of page

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.

top of page

For More Information

More information and related documents are on the Transportation and Air Quality Web site at:


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
E-mail: wilcox.rich@epa.gov

top of page

This page is maintained by EPA's Office of Transportation and Air Quality (OTAQ).
For more: About Us | Get Email Updates | Browse the A to Z Subject Index.

Local Navigation

Jump to main content.