Vehicle inspection & maintenance (I/M) programs

Vehicle inspection and maintenance (I/M) programs require scheduled testing of a vehicle’s tailpipe and evaporative emissions to determine the effectiveness of its emission controls. I/M programs are federally mandated under the 1990 Amendments to the Clean Air Act for areas with particularly poor air quality; program areas are identified based on criteria such as air quality classification, population, and/or geographic location (US EPA-IM resources). Programs can also be implemented at the discretion of state and local governments. Program design varies by location, although most I/M programs for modern, advanced technology vehicles use on-board diagnostic computer tests (US EPA-Vehicle OBD, US EPA-State IM Programs).

Expected Beneficial Outcomes (Rated)

  • Reduced emissions

Other Potential Beneficial Outcomes

  • Improved air quality

Evidence of Effectiveness

There is some evidence that vehicle inspection and maintenance (I/M) programs reduce emissions from light duty cars and trucks (, , , Eisinger 2005, Samoylov 2013, Austin 2009). However, additional evidence is needed to confirm effects of I/M programs for modern, advanced technology vehicle fleets.

I/M programs can improve air quality by reducing carbon monoxide, carbon dioxide, hydrocarbon (, , Eisinger 2005) and nitrogen oxide emissions (Samoylov 2013). Enhanced I/M programs, similar to Southern California’s program, can reduce older light duty motor vehicles’ hydrocarbon exhaust emissions by 14-28% (Eisinger 2005), and cars’ carbon monoxide emissions by 26% (). I/M programs may motivate pre-test repair work, improve repair effectiveness (Eisinger 2005), and create incentives for manufacturers to improve the emission characteristics of their vehicles, which would reduce emissions more than the amount attributed to existing programs ().

Variable timing I/M programs that target vehicles with a higher likelihood of being high polluters, based on characteristics such as vehicle age, odometer reading, engine size, or previous emission test results, can be significantly more cost-effective than non-targeted annual or biennial retesting programs (, , , Samoylov 2013).

Historically, I/M program costs have varied significantly with program design, stringency, and test equipment. Currently, however, most I/M programs use lower cost on-board diagnostic computer tests for modern vehicles (US EPA-Vehicle OBD). Inspection costs account for over two-thirds of the total cost of most programs, the remaining costs for actual vehicle repairs are borne by vehicle owners (). In most states with I/M programs, vehicles that are not repaired cannot be registered (US EPA-IM resources); this may contribute to disparities in access to transportation.

Impact on Disparities

Likely to increase disparities

Implementation Examples

As of 2016, the US Environmental Protection Agency (US EPA) lists vehicle inspection and maintenance programs in 31 states and Washington DC (US EPA-State IM Programs).

Implementation Resources

US EPA-IM resources - US Environmental Protection Agency (US EPA). State and local transportation resources: Vehicle emissions inspection & maintenance (I/M).

US EPA-Vehicle OBD - US Environmental Protection Agency (US EPA). Vehicle emissions on-board diagnostics (OBD).

Citations - Evidence

* Journal subscription may be required for access.

Harrington 2000* - Harrington W, McConnell V, Ando A. Are vehicle emission inspection programs living up to expectations? Transportation Research Part D: Transport and Environment. 2000;5(3):153-72.

Dehart-Davis 2002* - Dehart-Davis L, Corley E, Rodgers MO. Evaluating vehicle inspection/maintenance programs using on-road emissions data: The Atlanta reference method. Evaluation Review. 2002;26(2):111-46.

US EPA-IM resources - US Environmental Protection Agency (US EPA). State and local transportation resources: Vehicle emissions inspection & maintenance (I/M).

Washburn 2001* - Washburn S, Seet J, Mannering F. Statistical modeling of vehicle emissions from inspection/maintenance testing data: An exploratory analysis. Transportation Research Part D: Transport and Environment. 2001;6(1):21–36.

Bin 2003* - Bin O. A logit analysis of vehicle emissions using inspection and maintenance testing data. Transportation Research Part D: Transport and Environment. 2003;8(3):215–27.

Moghadam 2010* - Moghadam AK, Livernois J. The abatement cost function for a representative vehicle inspection and maintenance program. Transportation Research Part D: Transport and Environment. 2010;15(5):285–97.

Eisinger 2005 - Eisinger DS. Evaluating inspection and maintenance programs: A policy-making framework. Journal of the Air & Waste Management Association. 2005;55(2):147–62.

Samoylov 2013 - Samoylov AV. Improvement of the efficiency of vehicle inspection and maintenance programs through incorporation of vehicle remote sensing data and vehicle characteristics. Atlanta: School of Civil and Environmental Engineering, Georgia Institute of Technology (GT); 2013.

CVEIMP 2001* - Committee on Vehicle Emission Inspection and Maintenance Programs (CVEIMP), Board on Environmental Studies and Toxicology, Transportation Research Board, National Research Council. Evaluating vehicle emissions inspection and maintenance programs. National Academies Press; 2001.

Austin 2009 - Austin TC, McClement D, Roeschen JD. Evaluation of the California Smog Check Program Using Random Roadside Data. California Air Resources Board, California Bureau of Automotive Repair. Report No. SR09-03-01. 2009.

US EPA-Vehicle OBD - US Environmental Protection Agency (US EPA). Vehicle emissions on-board diagnostics (OBD).

Citations - Implementation Examples

* Journal subscription may be required for access.

US EPA-State IM Programs - US Environmental Protection Agency (US EPA). Vehicle emissions inspection and maintenance (I/M): Tampering, warranty, state websites and program evaluations.

Date Last Updated

Jun 4, 2015