Evaluating Vehicle Emissions Inspection and Maintenance Programs 

Executive Summary 

National Academy of Sciences 2001

MOTOR VEHICLES ARE a major source of air pollution on urban, regional, and national scales. Programs to control their emissions have focused on setting emissions standards for new vehicles, resulting in engineering and design improvements in emissions-control systems.

Inspection and maintenance (I/M) programs have been instituted in many jurisdictions to ensure that those controls operate properly throughout the life of a vehicle. These programs are implemented in areas violating federal air-quality standards (nonattainment areas) and in other areas seeking to improve air quality. The inspection typically involves regularly scheduled exhaust tests measuring carbon monoxide (CO), hydrocarbons (HC), and sometimes nitrogen oxides (NO.) emissions. I/M tests also include a visual inspection of the components controlling evaporative and exhaust emissions and may include a functional gas-cap test and a pressure test of the evaporative emissions-control system. The U.S. Environmental Protection Agency (EPA) has oversight and developmental responsibility for I/M programs, which are implemented by state agencies.

Evidence suggests that IM programs have been less effective than anticipated. This concern prompted Congress to request this study in its fiscal 1998 appropriations to EPA. In response to this request, the National Research Council (NRC) convened the Committee on Vehicle Emission Inspection and Maintenance Programs to conduct this study. Phase I of the study, presented in this report, examines the criteria and methodology for evaluating I/M programs and assesses their effectiveness in reducing vehicle emissions. Phase 2 will evaluate several types of I/M programs in more depth. The study charge also calls for the committee to make recommendations for improving I/M programs. The committee recommends some improvements in this report and will address others in phase 2.

In carrying out its charge for this report, the committee reviewed passenger-car and lighttruck emissions (the emissions typically targeted by I/M programs) within the context of overall emissions from mobile sources and other anthropogenic sources. Emissions-control technologies and testing techniques were considered, together with how changes in these factors might affect I/M programs. The committee also reviewed methods to estimate emissions reductions, and it examined previous evaluations of these reductions and other criteria important for evaluating such programs. 

FINDINGS AND RECOMMENDATIONS

The committee found that I/M programs have generally achieved less emissions reductions than originally projected by EPA's Mobile Source Emissions Factor (MOBILE) model and the California Air Resources Board Emissions Factor (EMFAC) model. These model-predicted reductions are important because they serve as part of the formal basis for crediting emissions reductions within state implementation plans (SIPS).

1 Independent and state-sponsored evaluations of ongoing I/M programs have estimated that the emissions reductions attributable to these programs are from zero to about one-half of the reductions predicted by the models. 
2 This figure is estimated using in-use vehicle emissions data, such as remote sensing, random roadside vehicle testing, and I/M emissions testing. The committee concluded that these data provide the best estimate of Ws effectiveness. Evaluations that rely on model predictions of emissions reductions using few or no in-use data are not accurate. This conclusion is based on a small number of peer-reviewed studies, and the methods used to make these estimates must be improved.

Despite the smaller-than-forecasted benefits from IM programs, the committee still sees a great need for programs that repair or eliminate high-emissions vehicles (commonly called high-emitting vehicles or high emitters) froth the fleet, given the major influence of this small fraction of the fleet on total emissions and air quality. However, I/M programs should improve the way they identify vehicles in need of repair and verify repairs. Improvements are also needed in the methods used to evaluate the impacts of these programs.

The use of the MOBILE and EMFAC models to predict emissions-reduction benefits from I/M programs in the development of air-quality-attainment plans indicates a flaw in the SIP process. EPA has granted states substantial emissions-reduction credits for I/M programs without the need to verify the extent to which the predicted emissions reductions are actually occurring. That situation creates a regulatory disincentive for states to evaluate the actual emissions-reduction benefits from I/M programs. Such an evaluation might reveal a shortfall in a state's emissions-reduction benefits and trigger requirements for SIP revisions.

The committee recommends that the crediting of emissions-reduction benefits for I/M programs, as with other emissions-control strategies, should be tied to the actual emissions reductions produced by these programs. Emphasis on observational data and empirical evidence has been inadequate in most aspects of I/M program evaluations. Rigorous scientific and technical analyses have been lacking in supporting decisions related to program implementation. EPA should expand its use of outside experts and publication of analyses in peer-reviewed literature to address that deficiency. Improvements are especially needed in the quantification of I/M program impacts based on more data-intensive approaches. These evaluation methods and their applications to estimate emissions benefits of state I/M programs should be reviewed independently and be disseminated to policy makers and the public.

¹ SIPS describe the strategies that regions in noncompliance with National Ambient Air Quality Standards (NAAQS) use to come into compliance.

The estimated emissions reductions are dependent on the pollutant and version of the model used for comparison. They are lowest for test-and-repair idle test programs and highest for hybrid or centralized transient test programs. Prospective Estimates of Emissions Reductions from IM Programs

Findings

On the basis of evaluations by states and by independent researchers, the committee found that I/M programs provide much lower benefits than estimated by the models. The MOBILE model estimates that a fully implemented enhanced I/M program3 would produce overall emissions reductions of 28% for HC, 31 % for CO, and 9% for NO. .4 Reasons for overstating emissions reductions include the following:

• Overestimation of the deterioration of vehicle-emissions performance (which overestimates potential benefits from I/M-induced emissions repairs).
• Inadequate representation of the behavior of motorists and mechanics.
• Overestimation of compliance with the program and the effectiveness of repairs.
• Overestimation of the ability to identify high-emitting vehicles.
• Incomplete implementation of some components of I/M programs (e.g., effective evaporation tests and inclusion of all older vehicles).

Recommendations

EPA and states should expect lower emissions-reduction benefits from I/M programs as currently configured. In general, models projecting emissions reductions from I/M programs should be improved to reflect actual reductions more accurately. States should perform periodic on-road sampling and evaluations of emissions reductions and compare those observations with modeled forecasts used in SIPS. To the extent that states are allowed to use default parameters in emissions models to forecast I/M emissions reductions for SIP credit, the default values of key parameters (e.g., compliance rates and repair effectiveness) should be more pessimistic (i.e., forecast lower emissions reductions) than those currently used. That might help to create an incentive for states to provide evidence that their programs achieve greater emissions reductions than specified by the default settings in the model.

High-Emitting Vehicles

Findings

A small, malfunctioning fraction of the fleet contributes a substantial proportion of overall vehicle emissions. Typically, less than 10% of the fleet contributes more than 50% of the emissions for any given pollutant Emissions reductions are skewed; a relatively small share of the vehicles failing an I/M test contributes a large proportion of total excess emissions

' Enhanced I/M programs are required in areas classified in "serious," "severe," or "extreme" nonattainment of National Ambient Air Quality Standards.

° The discussion here refers to analysis that was performed in 1992 using the version of the model known as MOBILE4.1. (emissions above the standard for failing a vehicle), while vehicles with emissions just above the threshold for test failure (so-called "marginal emitters") often have only a small reduction in overall emissions after repairs or, in some cases, actually have an increase in emissions after repairs. Thus, the largest potential reductions in emissions from I/M programs are associated with a small number of high-emitting vehicles.

Studies that combine data for vehicle ownership, high-emitter frequency, and income levels suggest a strong link between low household income and the likelihood of owning a high-emitting vehicle. Studies also show that between 10% and 27% of vehicles that fail an I/M test never pass the test. Their exact fate has not been well characterized, although some have been found to be still in operation in I/M areas in some states more than a year after their last test. More study of this issue is needed to determine how serious this problem is and what policies . will improve it.

Recommendations

1/M programs should focus primarily on identification, diagnosis, and repair of the highest-emitting vehicles along with verification of those repairs. A number of testing or identification regimes can identify high-emitting vehicles, including traditional I/M programs testing all vehicles, programs targeting certain vehicles for more or less frequent testing, and remote sensing. States should be given flexibility to choose a regime that meets their emissions reduction goals at the lowest cost to the public.

The focus on high-emitting vehicles should extend to promoting policies that seek effective repair or removal of all such vehicles. 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. Clearly, further research is needed to design the means to reduce high emitters in ways that are effective as well as socially and politically acceptable. States would have to evaluate which policies are the most cost-effective and acceptable ways of obtaining emissions reductions from high-emitting vehicles.

The committee is aware that identification of high-emitting vehicles is problematic and that the designation is relative. The sense of the committee is that more needs to be known about the cost-effectiveness of setting different emissions cutpoints,5 including the value of repairing vehicles with emissions only marginally higher than current cutpoints, to determine optimal cutpoints for vehicle tests.

Evaluating I/M Emissions Reductions

Findings

Official biennial evaluations of enhanced I/M programs required by the Clean Air Act Amendments of 1990 have not been completed by the majority of states required to perform them. The guidelines developed by EPA for performing these evaluations are limited to a single

The emissions levels that define whether a vehicle passes or fails are called cutpoints. method, which compares an I/M program with a benchmark I/M program. These guidelines are being revised and expanded. Most past evaluations have been performed by state agencies in response to state requirements for estimates of emissions-reductions benefits or by independent researchers interested in the same issue.

The primary data sources for evaluation of emissions-reduction benefits are test data from I/M programs, remote sensing of on-road vehicles, and roadside testing of on-road vehicles. Vehicle registration data are also important for estimating changes in the fleet over time. There are three approaches for using those data to determine emissions-reduction benefits. The "reference method" compares vehicle emissions in the program area with those in some reference area, which can be a benchmark I/M program or a non-I/M area. The "step method" compares emissions of vehicles tested under a newly-instituted I/M program with emissions of vehicles in . the same area that have yet to be tested under the new program. The "comprehensive method" tracks changes in emissions for vehicles that pass the test, those that initially fail and then pass, and those that fail and never pass.

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 differences between regions in which emissions would be expected to vary regardless of the presence or absence of an I/M program. In addition, using data on repaired vehicles collected as part of the I/M program to estimate the emissions-reduction benefits might not account fully for noncompliance with the program or for repairs made in anticipation of the I/M test.

Recommendations

EPA should provide additional guidance for carrying out LIM evaluations. The agency is commended for beginning this work, and the committee recommends that it be expanded to include additional methods of evaluation. EPA's guidance should be based on sound measurement and statistical evaluation methods and be peer reviewed, The agency should address comments gathered during the review of these evaluation methods. In addition, EPA should publish aspects of these evaluations in professional journals so that they can be reviewed further and disseminated.

The committee recommends that EPA and states ensure that some programs undergo comprehensive, long-term evaluations using multiple data sources and analytic techniques. I/M programs that undergo repeated, in-depth evaluations using multiple data sources and methods can potentially help improve the design of I/M programs and evaluation process nationally. Questions about the fate of vehicles that fail their I/M test, the durability of vehicle repairs, or the impact of I/M programs on vehicle registration and ownership patterns can be answered only through well-designed, comprehensive evaluations using a number of data sources.

Independent researchers should perform parts of these comprehensive evaluations. As stated previously, these full evaluations should be peer reviewed independently by experienced researchers, and EPA should pursue publishing some aspects of these evaluations in professional journals. Because such evaluations are resource-intensive, EPA should select several programs for such treatment and should support a portion of this work. The committee recognizes that not all jurisdictions will 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. The method should not rely on the MOBILE model but should be based on the best evidence from ongoing full evaluations and should include estimates of all components of emissions reductions achieved by I/M programs. These shortened evaluations will likely have to rely primarily on I/M program data and other local data for primary data sources, although on road data would be valuable. States should be urged to collect at least the amount of on-road data required under the rules for implementing enhanced I/M (0.1°l0 of the fleet). Evidence from full evaluations done in other locations might have to be incorporated to account for factors such as repair deterioration; ineffective, incomplete, or fraudulent repairs; pretest repairs; and program avoidance by changing vehicle registration.

A review committee should be established to advise EPA in the selection of shortened evaluation methods and in the selection of what information can be drawn from full evaluations to inform the shortened evaluation. The committee is concerned about the need for states to complete overdue evaluations and urges EPA to continue to develop these evaluation methods in a timely manner. 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/M program area that are avoiding testing. Although such indicators do not incorporate direct estimation of emissions reductions, they can help track the performance of a program over time and provide relatively concise indicators of program success. These performance indicators could include the following:

• An estimate of the total number of vehicles driven in the I/M region, the share of those vehicles that are eligible for inspection, and the share of those that are inspected.
• Failure rates by model year at the program cutpoints.
• Estimates of the average emissions of vehicles that pass and that fail inspections.
• Share of failing vehicles that actually get repaired to below program cutpoints and their average emissions rates before and after repair.
• Share of failing vehicles that do not ever pass the I/M test, their average emissions rates, and estimates of the number of those still driven in the area.
• The rate of repeat failures from one I/M cycle to the next.
• Estimates of the actual number of high emitters on the road.

Research Issues in I/M Evaluation

Findings

Many critical factors that have large effects on the emissions-reduction benefits from I/M programs are still unknown. An example is the length of time that repairs remain effective for a vehicle initially failing an I/M test. Estimates of the average effective duration for such repairs range from most of the 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. Full evaluations of at least a few I/M programs would shed light on many such issues.

Recommendations

Comprehensive evaluations of I/M programs should be used to research aspects thought to have major impacts on the emissions-reduction benefits from I/M programs These include the following aspects:.

• The distribution of the duration of repairs for vehicles that fail an initial I/M test.
• The extent of pre-inspection repairs.
• The extent to which temporary repairs and test fraud result in vehicles registering low emissions only for the purpose of passing an I/M test (the "clean for a day" phenomena).
• The fate of vehicles that fail their initial I/M test and never pass (unresolved failures).
• Consequences of I/M programs for nontailpipe HC reductions.

In addition, many of these unresolved issues relate to human responses to I/M programs, but only a few studies have attempted to examine those aspects. Comprehensive evaluations can shed light on the type and magnitude of behavioral responses, but separate behavioral studies are likely to be needed to provide additional important insight.

NOx and Particulate Matter (PM) Emissions

Findings

Future air-quality improvement programs are likely to place greater emphasis an controlling NO, and pM emissions. I/M programs traditionally have focused on inspecting vehicles for high CO or HC emissions or both. Loaded-mode emissions testing procedures that are needed to measure NO„ emissions have been introduced widely in only the past 5 years. Apart from smoking-vehicle complaint programs and some testing of heavy-duty diesel-truck smoke opacity, little effort has been made to identify and repair vehicles with high emissions of exhaust PM.

Currently, there are few assessments of I/M program effectiveness in reducing emissions of NO„ and PM pollutants. Although diesel engines area minor source of CO and HC, they are significant contributors to mobile-source NO„ and PM emissions.

Recommendations

I/M programs should clearly state which pollutants they are seeking to reduce. Different types of repair actions and different mechanic training programs are needed for I/M

6 A loaded-mode test involves testing vehicle emissions while the vehicle is on a dynamometer that simulates the load a vehicle is under during on-road driving. programs that focus on reducing NO, and PM emissions. Because heavy-duty diesel vehicles are a significant source of NOx and PM, I/M programs that target these pollutants might have to incorporate heavy-duty diesel vehicles to a greater extent.

Remote Sensing

Findings

Remote-sensing measurements are an excellent source of fleet-average CO and HC emissions data. Remote sensing can also be a useful screening tool to identify vehicles likely to pass or fail conventional 1/M program tests. Although use of remote sensing is increasing, its capabilities remain underutilized in I/M programs

Combined remote-sensing and roadside pullover studies have shown that a high proportion of vehicles identified by remote sensing as high emitters of CO, HC, or both also failed roadside tests given immediately after the remote-sensing test. However, the fraction of high-emitting vehicles that escaped detection by remote sensing in these studies and the number that do not participate in conventional I/M programs are unknown.

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, and 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.

Greater attention must be paid to site selection and quality-assurance and quality-control issues in remote-sensing studies. Some prior studies have focused too heavily on the number of vehicles and sites sampled and have sacrificed quality in seeking large quantities of data.

To determine the ability of remote sensing to identify vehicles with high NO, emissions, combined remote-sensing and roadside pullover studies that focus on this pollutant should be conducted. An intercomparison of the ability of different remote sensors to measure NO. emissions accurately should also be performed.

An important research priority is the development and evaluation of remote-sensing capabilities for exhaust PM emissions. Further research is also needed to increase the number and types of roadside sampling sites where remote-sensing equipment can be deployed.

Onboard Diagnostics

Findings

The committee found that the current data set for evaluating the effectiveness of

OBDII for EM testing is inadequate. Contemporary onboard diagnostic (01313) equipment, included on 1996 and newer model-year vehicles, represents a technological innovation for monitoring the performance of emissions-control equipment on light-duty vehicles. Current CBD technology, known as OBDII, provides rapid verification of the operation of both exhaust and evaporative emissions-control components but does not measure emissions. It alerts motorists to potential problems by illuminating a malfunction indicator light (MIL) and provides mechanics with diagnostic information about the source of malfunctions, including malfunctions that are intermittent in nature (e.g., a misfire). OBDII also represents a potentially improved method for assessing evaporative emissions-control components. Given its current specifications for MIL warnings however, it is not clear whether OBDII can fulfill both objectives of alerting vehicle owners to potential vehicle malfunctions and serving as a testing device in I/M programs. In addition, it is not known how motorists will react to MIL illumination, especially when the vehicles are no longer under warranty.

The OBDII system could operate as designed by automobile manufacturers and still indicate OBD I/M test failures on vehicles with low emissions. The current specification is that the MIL will illuminate if a problem is detected that results in or could potentially result in emissions higher than 1.5 times the vehicle's emissions certification standard. Studies have shown that if OBDII were used to decide whether vehicles passed or failed an inspection, most OBDII failing vehicles would have emissions less than 1.5 times the standard. Current I/M programs typically have much higher cutpoints than 1.5 times the vehicle's certification standard. The OBDII failure point might be too low for a cost-effective and publicly acceptable I/M program especially for older OBDII vehicles. An alternative approach, such as tailpipe testing, might be needed for those vehicles.

Recommendations

An independent evaluation should be established, with appropriate funding, using researchers outside the agencies to review the effectiveness and cost-effectiveness of OBDII testing programs before moving forward with full implementation of OBDII rule requirements. The rule allows states up to 3 years to phase in OBD I/M, which is required to begin January 2002. The recommended evaluation should study the issues of intermittent failures and the value of repairing vehicles with low emissions to prevent an increase of emissions in the future. Failing a large number of vehicles with emissions below 1.5 times the certification standards could undermine a commitment to find high-emitting vehicles and ensure that they are repaired. An alternative to using OBDII as a failure criterion in I/M testing is to use it as an advisory tool to inform motorists of potential emissions problems. This option can be used while phasing in an OBDII I/M program. It may also be considered for OBDII vehicles when they become older. No matter how OBDII is used, a substantial effort by EPA is needed to help the public thoroughly understand this system. Besides the issues of intermittent failures and the value of failing marginal-emitting vehicles with malfunctioning sensors or monitors, studies of other issues related to OBDII should be done. Such issues include the following:

• The fraction of vehicles appearing in I/M lanes with MILS illuminated.
• The fraction of vehicles with MILS illuminated that do not fail the exhaust test or any evaporative test.
• The fraction of vehicles without MILS illuminated that fail the I/M test. • The response rates of consumers to MIL illumination in both the absence and the presence of an I/M program and in the absence of a warranty.
• The use of OBDII diagnostic information to identify vehicle repairs that have a high emissions-reduction potential and repairs that have only a marginal impact on emissions.
• The possibility for changes in the cutpoint settings on OBDII systems to allow OBDII to focus on high-emitting vehicles.
• . In the long-term, the promotion of actual emissions readings in future OBD systems.
• Methods for measuring actual emissions-reduction benefits from OBDII.

Use of the MOBILE Model

Findings

The SIP process mandated by the Clean Air Act and its amendments requires that modeling be used to predict emissions inventories and estimate benefits from I/M programs in future years. Based on comparisons with I/M program evaluations, predictions from the current version of the MOBILE model have greatly overestimated the emissions benefits from I/M programs.

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 MOBILE for estimating I/M benefits should be reevaluated.

MOBILE should allow its users to readily incorporate data from current I/M program evaluations into assessments for future years. Key parameters (e.g., compliance rates, repair effectiveness, and OBDII I/M benefits) used to forecast I/M emissions-reduction benefits should have pessimistic default estimates resulting in lower expected reductions. States might then have an incentive to demonstrate, through evaluation, that their programs are better than the default. Further, embedded assumptions in the model should be simplified as much as possible so that assumed parameter values are transparent to users, and users can incorporate the latest available data into parameters!

In the long-term, the overall I/M estimation methodology in MOBILE should be substantially revised. Empirical data show that the underlying I/M modeling approach is flawed.

The committee recognizes the need to continue using models to estimate I/M program benefits in future years. It is important, however, to reiterate that evaluations of current program performance should rely as extensively as possible on empirical data (e.g., on-road vehicle emissions measurements) rather than on models such as MOBILE.

EPA is currently working on MOBILE6, which is expected to be less optimistic in its I/M benefit predictions.

Naturally, these input data should undergo some type of evaluation and approval process so that the resulting emissions estimates are credible.

Importance of Cost-Effectiveness and Public Response to IM

Findings

Although emissions reductions are central to any evaluation of I/M programs costs are inextricably linked to emissions reductions, making cost-effectiveness a critical evaluation criterion. For example, costs influence the behavior of vehicle owners and repair technicians, thereby affecting the emissions reductions achieved. The emissions reductions and the associated costs must both be considered in the design and improvement of I/M programs, and in the determination of whether effort is best directed at I/M or at alternative ways of reducing emissions.

Another important consideration is public concern about new technologies, such as OBDII or remote sensing, that are increasingly used in I/M programs. For example, confusion about what the MIL is conveying to drivers could impede the use of OBDII in I/M tests. Confusion about new technologies could reduce public and political support for their introduction into I/M programs and/or reduce their effectiveness.

Recommendations

I/M programs can be improved by identifying ways to make them more cost-effective and more readily understood and by easing the testing burden for vehicle owners. States should be encouraged to develop and implement cost-effective means for finding and repairing high-emitting vehicles. Analysis of cost-effective measures, however, must take account of the effect of I/M program requirements on owners' behavior. Some of the issues that deserve further research include the following:

• The roles of repair cost waivers in I/M programs. I/M programs typically devote considerable money and effort to finding failing vehicles. Once a vehicle is identified as a very-high-emitting vehicle, that vehicle should be repaired, sold out of the area, or scrapped. Vehicle scrappage programs and repair assistance programs are examples of policies that could be used to accomplish such a goal. The most cost-effective policies may differ by region.
• The use of emissions profiles for determining testing frequency. There is already growing evidence that reducing the frequency of testing vehicles with a low probability of failure, including exemption of recent model-year vehicles from regular testing, is very cost-effective. On the other hand, increasing the inspection frequency of vehicles with a high probability of failure and/or those with high repair deterioration should be investigated to determine its cost-effectiveness for identifying high emitters.
• The durability of emissions-control systems. Encouraging the production of vehicles with more robust emissions-control systems through the use of extended warranties and new-vehicle compliance programs may be an alternative approach to maintaining low emissions throughout a vehicle's lifetime.
• Understanding and quantifying owners' responses to RM regulations. For example, not enough is known about the extent of old-vehicle scrapping in response to I/M or of program avoidance and other types of noncompliance among different socioeconomic groups.
• The cost and emissions consequences of enforcement efforts. Greater enforcement of existing regulations may be a cost-effective way to improve program performance.
• More effective means of public outreach and education. New approaches to providing information to the public about new technologies that may be incorporated in I/M programs should be developed and studied. Priority should be given to concerns regarding remote sensing and OBDII.

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This prepublication version of Evaluating Vehicle Emissions Inspection and Maintenance Programs has been provided to the public to facilitate timely access to the committee's findings. Although the substance of the report is final, editorial changes may be made throughout the text and citations will be checked prior to publication. The final report will be available through the National Academy Press in the summer of 2001.

Committee on Vehicle Emission Inspection and Maintenance Programs
Board on Environmental Studies and Toxicology
Division on Earth and Life Studies
Transportation Research Board
National Research Council

National Academy Press Washington, D.C. NATIONAL ACADEMY PRESS 2101 Constitution Ave., N.W. Washington, D.C. 20418

NOTICE:
The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This project was supported by Cooperative Agreement CX 827224-01-0, between the National Academy of Sciences and the U.S. Environmental Protection Agency. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project.

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COMMITTEE ON VEHICLE EMISSION INSPECTION AND MAINTENANCE PROGRAMS

RALPH J. CICERONE (Chair), University of California, Irvine, California DAVID T. ALLEN (Vice Chair), University of Texas at Austin, Austin, Texas MATTHEW J. BARTH, University of California, Riverside, California HUGH ELLIS, Johns Hopkins University, Baltimore, Maryland GERALD GALLAGHER, J Gallagher and Associates, Inc., Englewood, Colorado DEBORAH GORDON, Transportation Consultant, Los Angeles, California ROBERT HARLEY, University of California, Berkeley, California HAROLD HASKEW, Harold Haskew and Associates, Inc., Milford, Michigan DOUGLAS R. LAWSON, National Renewable Energy Laboratory, Golden, Colorado VIRGINIA MCCONNELL, Resources for the Future, Washington, D.C. ALISON K. POLLACK, ENVIRON International Corporation, Novato, California ROBERT SLOTT, Massachusetts Institute of Technology, Cambridge, Massachusetts

Project Staff

K. JOHN HOLMES, Senior Staff Officer RAYMOND WASSEL, Senior Program Director for Environmental Sciences and Engineering NANCY HUMPHREY, Senior Staff Officer RUTH CROSSGROVE, Editor MIRSADA KARALIC-LONCAREVIC, Information Specialist RAMYA CHART, Project Assistant PAMELA FRIEDMAN, Project Assistant

Sponsor

U.S. ENVIRONMENTAL PROTECTION AGENCY BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY

GORDON ORIANS (Chair), University of Washington, Seattle, Washington JOHN DOULL (Vice Chair), University of Kansas Medical Center, Kansas City, Kansas DAVID ALLEN, University of Texas, Austin, Texas IN GRID C. BURKE, Colorado State University, Fort Collins, Colorado THOMAS BURKE, Johns Hopkins University, Baltimore, Maryland GLEN R CASS, Georgia Institute of Technology, Atlanta, Georgia WILLIAM L. CHAMEIDES, Georgia Institute of Technology, Atlanta, Georgia CHRISTOPHER B. FIELD, Carnegie Institute of Washington, Stanford, California JOHN GERHART, University of California, Berkeley, California J, PAUL GILMAN, Celera Genomics, Rockville, Maryland DANIEL S. GREENBAUM, Health Effects Institute, Cambridge, Massachusetts BRUCE D. HAMMOCK, University of California, Davis, California ROGENE HENDERSON, Lovelace Respiratory Research Institute, Albuquerque, New Mexico CAROL HENRY, American Chemistry Council, Arlington, Virginia ROBERT HUGGETT, Michigan State University, East Lansing, Michigan JAMES F. KITCHELL, University of Wisconsin, Madison, Wisconsin DANIEL KREWSKI, University of Ottawa, Ottawa, Ontario JAMES A. MACMAHON, Utah State University, Logan, Utah CHARLES O'MELIA, Johns Hopkins University, Baltimore, Maryland WILLEM F. PASSCHIER, Health Council of the Netherlands, The Hague ANN POWERS, Pace University School of Law, White Plains, New York KIRK SMITH, University of California, Berkeley, California TERRY F. YOSIE, American Chemistry Council, Arlington, Virginia

Senior Staff

JAMES J. REISA, Director DAVID J. POLICANSKY, Associate Director and Senior Program Director for Applied Ecology RAYMOND A. WASSEL, Senior Program Director for Environmental Sciences and Engineering KULBIR BAKSHI, Program Director for the Committee on Toxicology ROBERTA M. WEDGE, Program Director for Risk Analysis K. JOHN HOLMES, Senior Staff Officer

TRANSPORTATION RESEARCH BOARD 2000 EXECUTIVE COMMITTEE
JOHN M. SAMUELS (Chair), Norfolk Southern Corporation, Norfolk, Virginia THOMAS R. WARNE (Vice Chair), Utah Department of Transportation, Salt Lake City, Utah ROBERT E. SKINNER, JR. (Executive Director), National Research Council, Washington, D.C. WILLIAM D. ANKNER, Rhode Island Dept. of Transportation, Providence, Rhode Island THOMAS F. BARRY, JR., Florida Department of Transportation, Tallahassee, Florida JACK E. BUFFINGTON, University of Arkansas, Fayetteville, Arkansas SARAH C. CAMPBELL, TransManagement, Inc., Washington, D.C. E. DEAN CARLSON, Kansas Department of Transportation, Topeka, Kansas JOANNE CASEY, Intermodal Association of North America, Greenbelt, Maryland JAMES C. CODELL III, Kentucky Transportation Cabinet, Frankfort, Kentucky JOHN L. CRAIG, Nebraska Department of Roads, Lincoln, Nebraska ROBERT A. FROSCH, Harvard University, Cambridge, Massachusetts GORMAN GILBERT, Oklahoma State University, Stillwater, Oklahoma GENEVIEVE GIULIANO, University of Southern California, Los Angeles, California LESTER A. HOEL, University of Virginia, Charlottesville, Virginia H. THOMAS KORNEGAY, Port of Houston Authority, Houston, Texas BRADLEY L. MALLORY, Pennsylvania Department of Transportation, Harrisburg, Pennsylvania MICHAEL D. MEYER, Georgia Institute of Technology, Atlanta, Georgia JEFF P. MORALES, California Department of Transportation, Sacramento, California JEFFREY R. MORELAND, Burlington Northern Santa Fe Railway, Fort Worth, Texas JOHN P. POORMAN, Capital District Transportation Committee, Albany, New York CATHERINE L. ROSS, Georgia Regional Transportation Agency, Atlanta, Georgia WAYNE SHACKELFORD, Gresham Smith & Partners, Alpharetta, Georgia PAUL P. SKOUTELAS, Port Authority of Allegheny County, Pittsburgh, Pennsylvania MICHAEL S. TOWNES, Transportation District Commission of Hampton Roads, Hampton, Virginia MARTIN WACHS, University of California, Berkeley, California MICHAEL W. WICKHAM, Roadway Express, Inc., Akron, Ohio JAMES A. WILDING, Metropolitan Washington Airports Authority, Washington, D.C. M. GORDON WOLMAN, The Johns Hopkins University, Baltimore, Maryland

Acknowledgment of Review Participants

This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the NRC's Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:

Thomas Austin, Sierra Research, Inc. Robert Frosch, Harvard University Jay Gordon, Gordon-Darby, Inc. Thomas Hubbard, University of Chicago Roland Hwang, Natural Resources Defense Council Roberta J. Nichols, Ford Motor Company (retired) Robert Sawyer, University of California, Berkeley Joel Schwartz, Reason Public Policy Institute Donald H. Stedman, University of Denver

Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by Thomas Graedel, Yale University, and Richard Goody, Harvard University. Appointed by the National Research Council, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

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