@misc{30445,
  author = {Thomas P Wenzel and Nancy J Brown},
  title = {Can More Frequent Testing Improve I/M Program Effectiveness? Analysis of the Effect of Annual Testing in the Phoenix IM240 Program},
  abstract = {<p>In this report we examine the potential for additional emission reductions from adopting annual<br />rather than biennial testing in vehicle emission inspection and maintenance (I/M) programs. We<br />tracked a fleet of cars reporting for testing in two biennial cycles in the Phoenix IM240 program.<br />Using an assumption of linear deterioration following a passing I/M test, we found that annual<br />testing in the Phoenix program in 1996 would have resulted in an additional 45%, 48%, and 27%<br />reduction in HC, CO, and NOx emissions, respectively, over what occurred in the biennial<br />program. More stringent cut points under a biennial program would have resulted in greater<br />emission reductions, but with higher fail rates. Tighter cut points can also be applied to the<br />annual program. In fact, an annual program might ease the progression to tighter cut points by<br />resulting in relatively lower failure rates per test than biennial programs.

<br />A small number of cars were identified that were given three I/M cycles, each roughly one year<br />apart, in Phoenix. This group of vehicles had higher overall emissions and may not be<br />representative of the whole fleet. However, these cars appear to have the same HC and CO<br />emissions, but slightly lower NOx emissions, after two years as cars tested biennially. This<br />result suggests that our assumption that emissions after annual testing would deteriorate at the<br />same rate as observed in biennial testing may be optimistic. The findings from our analyses<br />suggest that test-to-test emissions variability is a limitation of existing I/M programs, and is<br />preventing them from properly identifying some vehicles with broken or malfunctioning<br />emissions controls and ensuring that they are repaired. In theory, more frequent testing of<br />suspected high emitters could help address this problem. One strategy that may work is to use<br />remote sensing to identify suspected high emitters, and require that they come in for off-cycle<br />testing, as frequently as necessary.

<br />Arizona remote sensing data provide additional evidence that a significant benefit results from<br />annual testing of older cars. Remote sensing measurements made in Phoenix of vehicles tested<br />biennially under the Phoenix enhanced IM240 program and of vehicles tested annually under the<br />Tucson two-speed idle program show interesting results. While newer vehicles from Phoenix<br />have lower emissions than those from Tucson, as one might expect from the enhanced program,<br />the older vehicles from Phoenix have higher emissions than those from Tucson. Phoenix<br />vehicles over seven years old had emissions 37% to 47% higher than Tucson vehicles of the<br />same age.

<br />We conclude that more attention should be paid to promptly identifying and properly repairing<br />the high emitters found in the older portion of the vehicle fleet.</p>},
  year = {2001},
  month = {06/2001},
  language = {eng},
}