Policy Study

Checking up on smog-check

A Critique of Traditional Inspection and Maintenance Programs

Executive Summary

Efforts to reduce unhealthful air emissions from cars and light trucks have a long regulatory history. Inspection and Maintenance programs (I/M), first introduced in the Clean Air Act of 1963, have evolved into a core component of our national policy to reduce mobile source emissions.

I/M programs typically require that all passenger vehicles (cars and light trucks) undergo periodic testing to determine whether their emission-control systems are performing acceptably. Traditional I/M programs involve inspections either annually or biennially, with inspection protocols that can range from relatively simple and inexpensive tailpipe testing to more complex and expensive dynamometer testing.

Few people dispute either the need or the desire to reduce mobile source emissions in society’s quest for cleaner air. However, many people question the central position given to traditional I/M programs in the mobile-source emissionreduction framework of national air quality policy.

Data now demonstrate the ineffectiveness of traditional I/M programs as a method of insuring that vehicle emission systems are kept in good working order. This poses a critical question in a framework of limited resources. How much money should be spent on rituals that have produced only modest benefits? Are there alternative programs that might be more successful in cleaning up polluting vehicles?

Recent research into automobile emission characteristics has demonstrated that some fundamental ideas behind traditional I/M programs are flawed, including assumptions that presume all cars are equally likely to pollute; all cars need to be tested; a universal focus on reducing marginally high-emitting vehicles is more important than targeting only very high-emitting vehicles; and behavioral incentives are less important than technological standard-setting. On the contrary, research indicates that the distribution of vehicle emissions is highly skewed, with a minority of vehicles producing a majority of emissions. Other evidence shows that this high-emitting group can be identified with a fairly broad range of techniques and that drivers of these vehicles can be given incentives that lead to either vehicle repair or retirement. Still other evidence shows that trying to repair marginal emitters can actually produce higher emission levels, rather than lower them.

These data point to a need for changing the focus of I/M programs to concentrate on identifying and repairing extreme- emitters. A successful program will need to develop methods to ease economic impacts on lower-income people who may have little economic choice but to operate extreme-emitting vehicles. New programs need maximum flexibility regarding choice of emission testing technology as fits each area’s needs. States need to look beyond the I/M paradigm to develop a system that takes human behavior into account, and shifts the incentive structure from “clean for a day,” to “clean every day.” Finally, states need to implement some method of validating I/M program performance, to confirm that hoped-for emission reductions are being realized.


Kenneth Green, D.Env., is Director of the Environmental Program at Reason Public Policy Institute and an expert reviewer for the Intergovernmental Panel on Climate Change (IPCC)'s most recent report on climate change. Dr. Green has published several peer-reviewed policy studies on climate change for RPPI, including A Plain English Guide to the Science of Climate Change, Climate Change Policy Options and Impacts, Evaluating the Kyoto Approach to Climate Change, and A Baker's Dozen: 13 Questions People Ask About the Science of Climate Change. He received his doctorate in environmental science and engineering from UCLA in 1994.