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Do Inspection and Maintenance Programs do what they say they do?

By: David MacHaemish

  Some people think the I/M programs are a complete waste of time, the benefits small or non-existent, the cost too high. Critics challenge the methods used to calculate the benefits of the program. They also challenge the testing methods, claiming the results are too inconsistent.
  In an effort to challenge the ability of the Drive Clean tests to consistently measure emissions, independent researchers took a car to 24 different testing facilities in the Greater Toronto Area. The results of their tests varied wildly. Nine times their car failed the test, eleven times it passed. (In the other four cases the test facility refused to test the car without repairs. If the vehicle has some kinds of problems it can damage the test equipment, so all cars must first be fit enough to at least take the test.) These results would seem to call the whole program into question.
  Representatives from both Air Care and Drive Clean are confident that their tests are consistent. They do not believe that these results call their testing programs into question. Before they could accept that their tests are invalid they would need to understand why the test car gave such different readings.
  It may have been that the car was inconsistent, not the tests. In a letter to the editor of the Toronto Star Wheels section, David Crump, Director of the Drive Clean Office, wrote, "As [the author of the report] knows - and indeed, acknowledged in a meeting with me - this particular vehicle had an intermittent problem with its exhaust gas re-circulation (EGR) valve that the "investigators" knew beforehand would cause the emissions control system to malfunction periodically." If the car did have a valve that failed only sometimes, then inconsistent results should be expected.
  Procedures and policies are in place to ensure that the emissions tests are fairly and accurately done. Both programs audit their test centers. When a problem is found the staff are retrained to perform the test correctly. Neither program has disclosed a widespread problem. After reading reports written by program staff this author is confident that the test methods used are consistent with accepted practice in that field. It is reasonable to accept that the tests are sufficiently valid.
  There is a valid criticism of the methods used to calculate the benefits of the program. The benefit of an I/M program is calculated by looking at the number of cars that fail the test, are repaired, and are re-tested. The change between the two tests shows how much better (or occasionally, worse) the car is. To whatever degree the test results are inaccurate they will skew the results to make the program look better. If a vehicle fails an initial test because it idled too long, has work done on it, and subsequently passes a test, it will show an improvement. Thus, false failures tend to make the program look good.
  However, a false pass does not affect the overall results of the program. If a vehicle has an intermittent problem, or just came off a long highway drive, and happens to be working well enough, it may pass the test. That test result will show only as a pass, and will not figure into the benefit calculation.
  This introduces a concern because a poorly run I/M program will appear to be better than it is, will appear to be better than a well run program. That means it is doubly important to maintain effective and critical oversight of I/M programs.

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