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Project at a Glance

Project Status: complete

Title: Study of emissions deterioration, post-I/M tampering, and cost/effectiveness of the smog check program

Principal Investigator / Author(s): Austin Thomas C

Contractor: Sierra Research, Inc.

Contract Number: A6-220-64

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


California Senate Bill 1997 (Presley, 1988) requires that the State Air Resources Board and the California Highway Patrol commence inspecting heavy-duty motor vehicles for excessive smoke and other emissions-related defects, using test procedures suited for use in an intermittent roadside inspection program. The bill further provides that--with the concurrence of the Highway Patrol--these inspections may be conducted in conjunction with the Highway Patrol's existing safety and weight enforcement activities. SB 1997 passed the California Legislature in August 1988, and was signed into law by the Governor in September.

ARB has been studying the feasibility of an emissions inspection and maintenance (I/M) program for heavy-duty Diesel vehicles for some time. A previous ARB-sponsored study1* examined several alternative I/M program designs, recommending the roadside inspection procedure specified in SB 1997 as the most effective and least costly approach. That study estimated that such a program could reduce emissions from heavy-duty Diesel vehicles by more than 11 tons per day (TPD) of NOz1 8.7 TPD of unburned hydrocarbons, and 31 TPD of particulate matter in 1990, compared to what they would otherwise be. These values are equal to 2% of the NOx, 9% of the RC, and 26% of the particulate emitted by heavy-duty Diesel vehicles. The cost-effectiveness of this program for particulate matter was estimated at about $1,500 per ton, making it one of the most cost-effective Diesel particulate control techniques available.

Under an existing contract to provide I/M-related support, Sierra Research was asked to assist ARB in developing an implementation plan for a roadside inspection program for heavy-duty trucks. The major purpose of this study was to examine existing CHP operations and facilities and recommend how the Roadside Emissions Inspection Program could best be implemented, taking the existing activities into account.


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

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