Enhanced Vehicle Emission Testing: Building on I/M Success in Southeastern Wisconsin

By Christopher Bovee, DNR Bureau of Air Management

In December 1995 enhanced motor vehicle emission testing began in southeastern Wisconsin. This enabled the state's inspection and maintenance (I/M) program to meet I/M requirements in the federal Clean Air Act Amendments of 1990, which require enhanced I/M programs to be implemented in 83 cities within 23 states. The I/M program is currently operating in the following seven counties: Kenosha, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha.

Vehicle emission testing originally started in southeastern Wisconsin in 1984. This highly-effective program has prevented 40,000 tons of carbon monoxide and ozone-forming hydrocarbons from entering the air each year. It is an important reason why the federal air quality standard for carbon monoxide--which was exceeded 35 times between 1977 to 1984--was not exceeded even once in southeastern Wisconsin after 1984. Surveys have shown the I/M program is well-accepted by the public.

Despite these successes, improvements to the original I/M program were needed to address recurring exceedances of the ozone health standard in eastern Wisconsin. While the program's "idle test" was very effective for testing the carbureted pre-1981 model year vehicles, a more comprehensive test was needed to test newer vehicles with advanced computer-controlled emission control systems.

Furthermore, the original program did not test for emissions of evaporative hydrocarbons--vapors which escape from various points of the vehicle's fuel system. On a hot summer day these vapors account for about 40% of the total motor vehicle hydrocarbon emissions in southeastern Wisconsin.

These deficiencies prevented Wisconsin's original I/M program from realizing its full potential for improving air quality. Enhanced I/M was the next logical step.

Evolution, not revolution

The transition to enhanced I/M which occurred in December 1995 was an evolutionary rather than a revolutionary change. The basic program requirements did not change: Vehicles still are required to periodically undergo tests for excess emissions at high-volume test facilities. Vehicles failing a test still need to be repaired and retested. The counties subject to the program did not change. As before, no fee is charged for the test.

The major enhancement involved new test procedures which more effectively identify high-emitting vehicles. Improving repairs and public convenience were also major focuses of the enhancement effort. The major changes to the I/M program are summarized here.

Benefits of enhanced I/M

Enhanced I/M will achieve substantial emission reductions, including twice as much carbon monoxide reductions and three times more hydrocarbon reductions than the original I/M program could achieve. The enhanced program contributes about one-fourth of the emission reductions in Wisconsin's federally-required plan for achieving 24% reductions of volatile organic compounds (hydrocarbons) in the Milwaukee area.

Fixing cars is also one of the most cost-effective ways to clean the air. The U.S. Environmental Protection Agency estimates that enhanced I/M is at least 10 times more cost-effective than new controls on small and large industrial sources. The fuel saving realized by effective repairs has helped offset the cost of the repairs.

Major Changes to Wisconsin's I/M Program

  • IM240 test. This test replaced the idle test as well as the inspection for tampering with emission control equipment. The new test measures emissions as the vehicle is driven on a dynamometer through a driving cycle taking up to four minutes (240 seconds) which simulates actual urban driving. The cycle consists of various accelerations, decelerations and cruise speeds up to 57 miles per hour. The pass/fail standards are more lenient for older vehicles to account for vehicle wear and different emission control technologies.

  • Evaporative system tests. Starting December 1995 the program began checking gas caps for vapor leaks. The I/M program is planning to use more comprehensive evaporative system tests once the test procedures are developed by the U.S. Environmental Protection Agency. The anticipated tests are a "pressure test" which checks for leaks in the fuel system and a "purge test" which checks for proper routing of fuel vapors back to the engine.

  • Reduced testing frequency. Under the old program, vehicles six or more years old were tested every year upon registration renewal. The newer vehicles were tested every other year. Under the enhanced program, all vehicles are tested upon registration renewal only every other year. Doing the test right is better than doing it often. Vehicles six or more years old have been and still are tested after change of ownership.

  • Expanded network and hours. The original network of 11 test stations with 31 lanes increased to 12 stations with 44 lanes. The hours open for testing increased from 45 hours to 60 hours per week.

  • Heavier vehicles tested. The maximum weight for required testing was raised from 8,000 pounds registered weight to 14,000 pounds gross vehicle weight rating, effective December 1995. During 1997 legislation was passed which reduced the maximum weight for required testing to 10,000 pounds gross vehicle weight rating. Diesel-powered vehicles and vehicles older than model year 1968 have been and still are exempt.

  • Repair information. Owners of failed vehicles receive detailed test results including diagnostic information. They also receive a report which provides statistics on the success of individual repair facilities in repairing vehicles to pass the retest.

  • Repair technician assistance. Two technical assistance centers are available to assist repair technicians in diagnosing vehicles which fail the initial test and a retest. A repair hotline is also available. The state and other interested parties have made a concerted effort to provide training opportunities for repair technicians.

  • Waiver criteria. For model year 1981 and newer vehicles, only repairs performed by technicians or facilities meeting minimum requirements can be applied to the repair cost limit for waivers. (The repair cost limit is currently $200 for Sheboygan County and $450 for the other six counties in the program area.) Vehicles can also be waived before the cost limit is reached if a "master automotive technician" at a designated technical assistance center confirms that no additional repairs could produce a passing result.

  • On-board diagnostic (OBD) check. Today's vehicles have OBD computers which monitor the vehicle's engine and emission control system. When the computer detects a malfunction, a light on the dashboard is illuminated and a code identifying the malfunction is stored in the computer for access by a repair technician. By identifying specific malfunctions, OBD enhances the repair industry's ability to diagnose and repair vehicles. (The first OBD systems were developed in the 1980's. The federal Clean Air Act requires OBD systems on all 1996 and newer light-duty vehicles and light-duty trucks.)

    The enhanced I/M inspection includes an OBD check, but repairs of identified malfunctions are currently not required. OBD checks, if found to be effective, may replace other enhanced I/M tests in the future.

For more information about the vehicle inspection/maintenance program, contact:

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Last Revised: Tuesday January 16 2007