ENVIRONMENT /POLLUTION TRAP : Designer Says New Device Spots Dirty Cars on Road : When hooked to a camera, it records license plates of emissions violators. Illinois is testing system; California has reservations.

Speed traps have long been a spoiler for motorists. Now, get ready for pollution traps.

Donald Stedman, a University of Denver chemistry professor, spent four days recently along Chicago’s busy Eisenhower Expressway testing a new system that he designed to spot badly polluting cars as they drive on entry or exit ramps.

Environmental officials here hope Stedman’s invention will one day become an integral tool in the fight against excessive exhaust emissions and reduce the need for costly and inconvenient emissions testing programs such as those required of motorists in the Chicago area as well as California.

“This has become so much more compelling now than three weeks ago,” said Stedman, referring to the recent spiraling cost of fuel. A car in need of a tune-up not only pollutes the air but also uses more gasoline.

Stedman’s contraption, known as Fuel Efficiency Automobile Test, or FEAT, beams an infrared light at tailpipe level across the ramp. A sensor on the opposite side of the ramp reads carbon monoxide and hydrocarbon emissions of vehicles that break the beam. Simultaneously, a video camera records license plate numbers and matches them with the readings.

In theory, the license data would be used to track down owners of any cars found to be in violation of federal emission standards. They could be ticketed or ordered to come to a center for further testing.

Previous research with the equipment led Stedman to conclude that a minority of cars causes the majority of auto-related pollution. He said that about 70% of vehicles seem to run clean enough to meet government guidelines, 28% sometimes exceed pollution limits and the rest are always in violation when the motor is running.

In total, about half of all toxic carbon monoxide emitted by vehicles in the Chicago area can be linked to a scant 8% of those on the road, according to his research. Pinpoint the small number of bad guys and you’ve gone a long way toward solving the car pollution problem, his methodology suggests.

That’s precisely the result that the Illinois Department of Energy and Natural Resources hopes can come out of Stedman’s research, which the agency is spending $50,000 to fund.

At present, all cars in Northern Illinois must be tested annually at state drive-in facilities. Stedman and his supporters question the value of such tests because they are done when cars are idling in neutral and don’t necessarily reflect how they operate under highway conditions.

“This is a split second in time, but it is real time,” Stedman said of his curbside testing device.

Bill Denham, research economist for the Illinois clean air agency, said random exhaust monitoring with FEAT could be far more effective than the present system.

“If you take the (on-site) test and the car goes out of tune a day later, the (clean air agency) won’t know it for a year,” Denham said. “ . . . This gives us the opportunity to test the car once a day, once a week or once a month.”

The cost of the current inspection program--$23 million a year and rising--could be halved, according to Denham’s crude calculations. More important, it could bring Illinois’ air quality in compliance with EPA standards.

Although Illinois officials see promise in FEAT, not everyone is sold on its value, including officials in California.

“Unless the test is done with some controlled circumstances, the results are fallible,” said William Sessa, spokesman for the California Air Resources Board. He cited such variables as a cold car or a car accelerating or decelerating as potentially skewing on-road test results. Last year, the California Air Resources Board used Stedman’s device to screen cars for carbon monoxide research, but the test was done under fixed, not random, conditions.

Undaunted, Stedman suggests that his California critics might be motivated by reasons other than science. “They made a political investment in the program they set up. They said it works. I’m saying it doesn’t,” he said.

He does concede that smog and emission control programs like the one now in use in California were considered state of the art when they were implemented a few years ago. Even his own device could be “antiquated in five years,” Stedman acknowledged.

“I liken it to the development of the microscope,” said Marc Pitchford, an atmospheric physicist with the Environmental Protection Agency’s Monitoring Systems Laboratory in Las Vegas, who helped Stedman get federal funding three years ago to build his pollution detector. “It doesn’t cure the disease directly, but it gives us a lot of information to help cure the disease.”

If Stedman’s research pans out, officials here say, cars zooming along ramps of the Eisenhower or other expressways could be making recurring appearances on the pollution watching “candid camera” in as little as five years.