“Passing the Test” – Human Behavior and California’s Smog Check Program

Abstract

We have analyzed data obtained from more than 11,000 vehicles inspected in California's random roadside surveys to assess the realworld characteristics of the in-use motor vehicle fleet and to test the effectiveness of California's inspection and maintenance (I/M) program. The low-idle emissions data from these surveys show that 10 percent of the fleet are responsible for about 60 percent of the exhaust hydrocarbons and also that 10 percent of the fleet (not necessarily the same vehicles) are responsible for about 60 percent of the carbon monoxide emissions. We also show that high emitters appear among all model years, and not just among old vehicles, as previously assumed. Old vehicles, on average, have higher idle emissions than new vehicles, but they contribute relatively little to the total idle emissions because there are so few on the road. We compare roadside survey results at I/M and non-l/M locations in California, and observe identical tampering and overall failure rates at the two types of locations. We also show that motorists are taking steps to “pass the test,” and that the high-emitting vehicles' idle-emissions performance and tampering rates in the roadside surveys are unaffected by the Smog Check test. These results imply that success in California's Smog Check program in reducing emissions will require consideration of human behavior and the attendant negative incentives inherent in the program as historically conceived. EPA's national tampering surveys also show little difference in tampering rates among areas with decentralized, centralized and no I/M programs. We therefore propose that an I/M “Shootout” be conducted to evaluate candidate programs for the next generation of I/M programs in the United States.