Evaluating Vehicle Emissions Inspection and Maintenance Programs (2001) / Chapter Skim
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convened the Committee on Vehicle Emission Inspection and Maintenance Programs to conduct this study. Phase ~ ofthe study, presented in this report, examines the criteria and metho(lology for evaluating I/M programs and assesses their effectiveness in reducing vehicle emissions.
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. ~ Independent and statesponsoredevaluations of ongoing I/M programs have estimated that the em~ssions reductions attributable to these programs are from zero to about one-half ofthe reductions predicted by the models.2 This figure is estimated using inuse vehicle emissions data, such as remote-sensing, random roadside vehicle testing, and T/M emissions testing.
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Prospective Estimates of Emissions Reductions from [/M Programs Findings On the basis of evaluations by states and by independent researchers, the committeefound thatI/Mprograms provide much lower benef Is than estimated by the models. The MOBILE model estimates that a filthy imple
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. High-Emitting Vehicles Findings A small, malfunctioning fraction of the fleet contributes a substantial proportion of overall vehicle emissions.
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However, any program designed to repair high-emitting vehicles might raise serious fairness concerns, because high emitters are more likely to be owned by persons of limited economic means. The committee recommends that policies be explored to provide financial or other incentives for motorists of high-emitting vehicles to seek repairs or vehicle replacement.
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Each data source and evaluation method has inherent advantages and disadvantages. For example, simple comparison of emissions data in one area with those in a reference area needs to correct for physical and socioeconomic sThe emissions levels that define whether a vehicle passes or fails are called cutpoints.
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The committee recognizes that not ad jurisdictions wiR be able to devote the resources needed to perform comprehensive evaluations using multiple sources of primary data. The committee recommends that guidelines for a shortened evaluation method also be developed and peer reviewed.
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Assumptions used in the shortened evaluation can then be continually improved as more evidence becomes available. Both the comprehensive and the shortened program evaluations should include a consistent set of performance indicators, such as the number of high-emitting vehicles driven in an I/Mprogram area that are avoiding testing.
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Estimates of the average effective duration for such repairs range from most ofthe benefits disappearing in less than 6 months to remaining for 2 years or more. Without better understanding of repair duration and other unknown factors, the full effect of I/M programs on vehicle emissions will remain uncertain.
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I/M programs traditionally have focused on inspecting vehicles for high CO or HC emissions or both. Loaded-mode emissions testing procedures6 that are needed to measure NOx emissions have been introduced widely in only the past 5 years.
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Recommendations Remote sensing should have an increased role in assessing motor vehicle emissions and I/M program effectiveness, determining the extent of pre-inspection repairs, andf estimating the extent of certain types of noncompliance. Remote sensing is also effective for identifying high emitters; however, its implementation into an I/M testing program should be an area of further research.
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An alternative approach, such as tailpipe testing, might be nee(led for those vehicles. Recommendations An independent evaluation should be established, with appropriate funding, using researchers outside the agencies to review the effectiveness arid cost-effectiveness of OBD testing programs before moving forward with fuR implementation of OBDI]
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Use of the MOBILE Mode! Findings The SIP process mandated by the Clean Air Act and its amendments requires that modeling be used to predict emissions inventories and estimate benef is from ]
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' These findings and the 2000 report Modeling Mobile-Source Emissions by the National Research Council suggest that there has been inadequate emphasis on data and empirical evidence in modeling I/M benefits. Recommendations The methodology used in MOBllEfor estimatingI/Mbenef ts should be reevaluated.
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There is already growing evidence that reducing the frequency of testing vehicles with a low probability offaiTure, including exemption of recent modelyear vehicles from regular testing, is very cost-effective. On the other hand, increasing the inspection frequency of vehicles with a high probability offailure and/or those with high repair deterioration should be investigated to determine its cost-effectiveness for identifying high emitters.
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For example, not enough is known about the extent of old-vehicle scrapping in response to T/M or of program avoidance and other types of noncompliance among different socioeconomic groups. · The cost and emissions consequences of enforcement efforts.
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