THE COSTS OF M IN I M - REFLECTIONS ON INSPECTION MAINTENANCE PROGRAMS/

To test the effectiveness of California's vehicle inspection/ maintena nce (I/M) program, exclusive of vehicle-owner intervention, a fleet of more than 1,100 vehicles that previously had failed California's Smog Check test were sent to randomly selected Smog Check stations in the Los Angeles area for covert inspections and repairs. The two-speed idl e test was used for repairs. For those vehicles that were repaired at the first inspection, their FTP emission reductions were 25%, 14%, and 11% for hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), respectively, although emissions testing for NOx was not perfor med at the Smog Check stations. Idle HC and CO emissions increased for 35% and 43% of the vehicles, respectively, after repairs. This data s et shows that most vehicles that fail the Smog Check inspection are on ly marginal emitters, with 61% and 44% of the total potential for HC a nd CO emission reductions, respectively, coming from only 10% of the v ehicles that currently fail the inspection. When the vehicles were ran k-ordered by idle emissions from dirtiest to cleanest, emission reduct ion costs for the highest-emitting 10% of the fleet averaged $1,100/to n and $250/ton for HC and CO, respectively, attributing all the costs to each pollutant exclusively. For the remaining vehicles, costs incre ased dramatically.