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Project at a Glance

Project Status: complete

Report Published May 1988:

Title: Heavy duty diesel vehicle inspection and maintenance study

Principal Investigator / Author(s): Weaver, Christopher S.

Contractor: Radian Corporation

Contract Number: A4-151-32

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


Heavy-duty diesel vehicles are responsible for significant emissions of oxides of nitrogen (NOx), unburned hydrocarbons (HC) and particulate matter (PM) in urban areas in California. As with other types of vehicles, poor maintenance and / or tampering with emissions controls can greatly increase these emissions. Up to now, however, diesel vehicles in most states have been exempt from any type of inspection and maintenance (I/M). such as California's Smog Check Program. This is due to the lack of a well-documented emissions test procedure for diesels, and to uncertainty as to the cost-effectiveness of such a program.

In order to address these issues, the California Air Resources Board (ARB) issued contract no. A4-151-32 to Radian Corporation, for a study which would:

* Quantify the extent of excess emissions from heavy-duty diesel vehicles due to malmaintenance and / or tampering;
* Develop and validate suitable I/M procedures for heavy-duty diesel trucks and buses; and
* Estimate the costs and emissions benefits of implementing a heavy-duty diesel I/M program.

The study results indicate: that excess emissions from heavy-duty diesels are significant; that suitable procedures for detecting high-emitting vehicles exist; and that a suitability designed I/M program could be very cost-effective compared to other diesel emissions control measures that have been adopted.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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