%0 Report
%A Thomas P Wenzel
%D 1999
%G eng
%T Using Program Test Result Data to Evaluate the Phoenix I/M Program
%! Report to the Arizona Department of Environmental Quality
%X <div>This report uses emissions test result data from 1997 to evaluate the effectiveness of the</div><div>enhanced I/M program in reducing vehicle tailpipe emissions in Phoenix, Arizona. The analysis</div><div>is based on a comparison of initial and final test results for individual vehicles that received their</div><div>initial I/M test in 1997. Two types of tests are performed on vehicles subject to I/M testing in</div><div>Phoenix; the idle and loaded idle test is required of 1980 and older vehicles, while 1981 and</div><div>newer vehicles must take the IM240 test. Significant differences between the two types of test</div><div>require that the emissions of the two fleets be analyzed separately.</div><div>&nbsp;</div><div>Arizona allows vehicles to fast pass or fast fail the IM240 test; in order to compare emissions of</div><div>vehicles tested over different portions of the IM240, we must convert these “short test” results to</div><div>full IM240 test equivalents. A relatively simple method to make this conversion is used; a</div><div>comparison of this method with other more detailed methods indicates that all methods tend to</div><div>underestimate full IM240 emissions using fast pass/fast fail emissions results. The analysis does</div><div>not consider the effect of the I/M program on reducing evaporative HC emissions.</div><div>&nbsp;</div><div>Comparison of initial and final IM240 tests indicates that the program is reducing the average</div><div>per vehicle emissions by 16% for HC, 17% for CO, and 7% for NOx, for the entire vehicle fleet.</div><div>After weighting per vehicle emissions by estimated annual miles traveled, the fleetwide</div><div>emissions reductions are 2.3 tons per day (14% reduction) for HC, 34 tons per day (15%</div><div>reduction for CO), and 2.3 tons per day (7% reduction) for NOx. CO and NOx reductions appear</div><div>to be substantially larger for cars than for light duty trucks. Per vehicle emissions of the loaded</div><div>idle fleet are reduced by 15% for HC and 23% for CO.</div><div>&nbsp;</div><div>About 11% of all vehicles fail their initial IM240 emissions test; the failure rate is slightly higher</div><div>for passenger cars (12%) than for light duty trucks (8%). The initial failure rate for the loaded</div><div>idle test is 37%. Of the vehicles that fail their initial test, only 70% received a final passing test</div><div>through March 1998; 30% did not receive a final passing test through March 1998. Because</div><div>waivered vehicles are not identified in the data, the actual percentage of No Final Pass vehicles is</div><div>likely to be closer to 26%. The percentage of No Final Pass cars is greater than the percentage of</div><div>No Final Pass trucks.</div><div>&nbsp;</div><div>The percent reductions in loaded idle emissions for Final Pass vehicles tend to increase by model</div><div>year, with larger reductions for newer vehicles. There is a large increase in percent reduction for</div><div>model year 1974 through 1980 vehicles, presumably due to stricter cutpoints applied to those</div><div>vehicles. The percentage reductions of IM240 Final Pass vehicles from model years 1981</div><div>through 1993 are fairly constant by model year. HC and CO emission reduction percentages</div><div>tend to increase after model year 1993.</div><div>&nbsp;</div><div>We use a relatively crude method to estimate total emissions and emission reductions in tons per</div><div>day for the loaded idle fleet, in order to estimate the tonnage reductions for the entire Phoenix</div><div>I/M program. We estimate that the program reduces the emissions of the fleet reporting for I/M</div><div>by 3.0 tons per day for HC, 38 tons per day for CO, and 2.6 tons per day for NOx. The majority</div><div>of the estimated emissions reductions comes from the IM240 fleet: 76% for HC, and 88% for CO</div><div>and NOx. The estimated percent reduction in total emssions is 15% for HC, 13% for CO, and</div><div>7% for NOx.</div><div>&nbsp;</div><div>The estimated effectiveness of the I/M program depends on whether the No Final Pass vehicles</div><div>have been permanently removed from the I/M area, or if they continue to be driven in the I/M</div><div>area. The effectiveness of the program on the IM240 fleet nearly doubles if one assumes that all</div><div>IM240 No Final Pass vehicles have been permanently removed from the area. Analysis of 1995</div><div>IM240 test data and remote sensing data indicate that about half of the No Final Pass vehicles</div><div>continue to be driven in the I/M area. If this information is correct for vehicles tested in 1997,</div><div>the 1997 I/M program resulted in a 22% reduction in HC and CO, and a 9% reduction in NOx</div><div>from the IM240 fleet. These percentage reductions are equivalent to 3.0 tons per day for HC and</div><div>NOx, and 48 tons per day for CO.</div><div>&nbsp;</div><div>Analysis of a single year of I/M program test data can only provide a partial understanding of the</div><div>program’s effectiveness in reducing emissions. Tracking of individual vehicles over several I/M</div><div>cycles can reveal important information on long-term effectiveness of vehicle repair, and</div><div>changes in the fleet reporting for I/M testing. In addition, an independent source of on-road</div><div>emissions tests, such as from a remote sensing measurement program, can provide additional</div><div>information on repair effectiveness, the effect of pre-test repairs on emissions, and the number</div><div>and emissions of vehicles avoiding the I/M program.</div>