The Congestion Mitigation and Air Quality Improvement Program: Assessing 10 Years of Experience -- Special Report 264 (2002)

The Clean Air Act Amendments (CAAA) of 1990 strengthened the link between transportation and the environment, toughening requirements for transportation projects to conform with air quality standards. In the following year, passage of the Intermodal Surface Transportation Efficiency Act (ISTEA) established the first federally funded transportation program explicitly targeting air quality improvement—the Congestion Mitigation and Air Quality Improvement (CMAQ) program (Nichols 1996, 133). In an introductory statement for the new ISTEA legislation, Senator Daniel Patrick Moynihan traced traffic congestion and air pollution to the “inefficient use of the automobile as a mode of transport” (Moynihan 1991, 11). Those who testified before the Senate Committee on Environment and Public Works noted that “four decades of straightforward adding to ‘supply’ by building more urban highway lanes or diverting demand through additional transit facilities had been tried—and has had at most a partial success” (Moynihan 1991, 4–5). Hence, approximately 4 percent of total funding for the 1992–1997 federal surface transportation program, or $6 billion, was earmarked for CMAQ projects that would offer alternatives to single-occupant vehicle (SOV) travel, improve travel efficiency as a means of addressing traffic congestion, and promote cleaner motor vehicles in the nation’s most polluted areas.

In 1998 the Transportation Equity Act for the 21st Century (TEA-21) reauthorized CMAQ for an additional 6 years (1998–2003) and increased its funding to a minimum of $8.1 billion. TEA-21 also included a request (see Appendix A) that the National Academy of Sciences conduct an evaluation of the CMAQ program. Hearings conducted during the reauthorization process had raised many issues that

prompted this request. How well is the program meeting its primary policy goal of improving air quality? Should more attention be paid to congestion alleviation as an important program policy goal in its own right and project eligibility broadened to include more traditional congestion mitigation measures, such as projects to expand highway capacity? Can desired program outcomes, such as reduced motor vehicle trips, travel, vehicle emissions, and pollutant concentrations, be measured? Can the program’s qualitative benefits be assessed? Are CMAQ projects cost-effective relative to other pollution reduction strategies? Should the program be broadened and project eligibility expanded to cover new pollutants and emission reduction strategies? To respond to the congressional request and address these questions, the Transportation Research Board (TRB) of the National Research Council (NRC) appointed the Committee for the Evaluation of the Congestion Mitigation and Air Quality Improvement Program. This report presents the committee’s findings and recommendations.

The remainder of this chapter begins with a brief introduction to the CMAQ program. A more detailed discussion of the study charge, an overview of the committee’s approach to the study, and a summary of the report organization are presented in the following sections.

From its inception, the primary policy focus of the CMAQ program has been on air quality improvement, reflecting the requirements placed on the transportation sector by the CAAA to help meet national air quality goals. The CAAA imposed strict deadlines for the achievement of National Ambient Air Quality Standards (NAAQS),¹ and required the transportation sector to contribute to emission reductions embodied in state implementation plans (SIPs)² to help meet air quality improvement targets in nonattainment areas (i.e.,

areas not in compliance with the NAAQS). The CMAQ program was closely linked to the provisions of the CAAA. It provided funding for states to use in nonattainment areas to help them comply with strict new conformity requirements and schedules. The program was focused on the criteria pollutants of greatest concern at the time the CAAA and ISTEA were passed—carbon monoxide (CO) and the ozone precursors, volatile organic compounds (VOCs) and oxides of nitrogen (NO_x) (FHWA 1992, 2).³

While the focus of the CMAQ program reflected the goals of the CAAA, its structure reflected the basic philosophy of ISTEA. Program goals were determined by the Federal Highway Administration (FHWA) and the Federal Transit Administration (FTA) in cooperation with the Environmental Protection Agency (EPA). Within broad guidance regarding project eligibility, however, decisions about project selection and implementation were the responsibility of the states and metropolitan planning organizations (MPOs), the key agencies for transportation planning in metropolitan areas. The program thus reflected ISTEA’s emphasis on strong local planning and decision making and an enhanced role for MPOs. The program was also viewed as a new partnership in which Congress joined with the states and local governments to fund a federal mandate (i.e., the requirements of the CAAA). In 1995 the National Highway System Designation Act authorized states to use CMAQ funds in maintenance⁴ as well as nonattainment areas (FHWA 1996a).⁵ This change reflected a realization that some level of funding was appropriate to both reward areas that had attained compliance and help them remain in compliance.

Reauthorization of the program occurred in 1998 with the passage of TEA-21, which reaffirmed CMAQ’s policy goal and focus on air quality improvement.⁶ Funding for the program was increased by 35 percent—approximately the same rate of increase as that of other federal-aid highway programs—to a minimum of $8.1 billion over the 6-year life (1998–2003) of TEA-21. Proposed revisions to EPA air quality standards that would have increased the number of areas in nonattainment status supported this funding increase (Gardiner 1997, 14).⁷ The legislation continued the policy change of 1995 that made maintenance as well as nonattainment areas eligible for CMAQ funding, and the apportionment formula was adjusted to reflect that change.⁸ The legislation also made nonattainment and maintenance areas for particulate matter (PM₁₀) explicitly eligible for CMAQ funding in recognition of the growing evidence of particulates’ adverse health effects (Heanue 1997, 20). The funding formula, however, was not modified to include particulates as a factor in apportioning CMAQ funds to the states. Finally, changes were made in project eligibility that are described in some detail in a subsequent chapter.

As noted earlier, during hearings on the reauthorization of ISTEA, questions were raised about the efficacy of the CMAQ program in reducing emissions and improving air quality (AASHTO Journal 1997a; AASHTO Journal 1997b). Some highway user groups objected

to the expenditure of highway funds for air quality projects, which, they maintained, were often costly and ineffective in reducing mobile source emissions relative to other strategies (Fay 1997, 43). Such groups proposed elimination of the mandatory set-aside of highway funds for the CMAQ program, consolidation of the funds into a streamlined surface transportation program, and greater flexibility for state and local transportation officials to set their own transportation priorities (Fay 1997, 43).⁹

Other transportation officials supported continuation of the CMAQ program, but noted that its congestion mitigation aspect had been lost with the program’s primary focus on air quality improvement (Smith 1996, 193). These officials called for greater emphasis on congestion mitigation as an important program goal, and recommended broadening eligibility to include more-traditional highway capacity expansion projects (e.g., freeway interchanges, lane widening) that, in their view, would relieve pollution-creating congestion (Smith 1996, 193–194).

Environmental groups advocated retention of the program because of its environmental benefits (funds are targeted to where the problems are), funding of federal mandates (clean air improvements), and support of projects that are not eligible for other federal program funding (Howell 1996, 205). They urged that CMAQ funds not be used for highway expansion projects, questioning the link between congestion mitigation and air quality improvement (AASHTO Journal 1997a; AASHTO Journal 1997c).¹⁰ Instead, they argued, the program should continue to focus on air quality and ensure that congestion mitigation projects meet long-term air quality goals (Howell 1996, 202).

Local governments supported reauthorization of CMAQ because it gave localities funding to help implement the federal mandate on clean air (Abramson 1996, 179). Moreover, they urged Congress to commit additional funds should the air quality standards for ozone and particulates be made more stringent, thus increasing the numbers of metropolitan areas in nonattainment (Abramson 1996, 178).

The U.S. Department of Transportation (USDOT) and EPA also supported reauthorization of CMAQ at increased funding levels in anticipation of more stringent air quality standards (AASHTO Journal 1997a; AASHTO Journal1997b). However, they recognized that more time was needed to experience and assess the overall benefits of the CMAQ program (Nichols 1996, 140; Heanue 1997, 29; AASHTO Journal 1997b).

Taking the different viewpoints summarized above into consideration, Congress decided to reauthorize the CMAQ program and seek an evaluation of its benefits and cost-effectiveness. The resulting legislative request identifies nine specific items for study:

• Task A—Evaluate the air quality impacts of emissions from motor vehicles.

• Task B—Evaluate the negative effects of traffic congestion, including the economic effects of time lost as a result of congestion.

• Task C—Determine the amount of funds obligated under the program, and perform a comprehensive analysis of the types of projects funded under the program.

• Task D—Evaluate the emission reductions attributable to projects of various types that have been funded under the program.

• Task E—Assess the effectiveness, including both quantitative and nonquantitative benefits, of projects funded under the program, and include in the assessment an estimate of the cost per ton of pollution reduction.

• Task F—Assess the cost-effectiveness of projects funded under the program with respect to congestion mitigation.

• Task G—Compare the costs of achieving the reductions in air pollutant emissions achieved under the program with those that would be

incurred if similar reductions were achieved by other means, including pollution controls on stationary sources.

• Task H—Include recommendations for improvements, including other types of projects, that would increase the overall effectiveness of the program.

• Task I—Include recommendations for expanding the scope of the program to address traffic-related pollutants that, as of the date of the study, were not being addressed by the program.

The study committee viewed Tasks A through C above as important to set the context for the study. However, the committee relied on existing studies and databases to address these items, instead of conducting an extensive evaluation of its own. The primary emphasis of the study was on the remaining Tasks, D through I, which go to the heart of assessing program performance and making recommendations for improvement.

In reviewing its charge, the committee drew a distinction between a program- and a project-level evaluation. At the program level, the key task is to determine whether program funds are being directed appropriately toward the intended goals—in this case air quality improvement and congestion mitigation—and with what effect. Another way of addressing this task is to examine whether there are other, more effective strategies for achieving these goals.

At the project level, the issues of effectiveness and cost-effectiveness, which feature so prominently in the congressional request, are highly context specific. The same strategy may have different effects in nonattainment areas with differing pollution problems. For example, a nonattainment area with a CO problem may select traffic flow improvement projects; decreasing stop-and-start traffic by smoothing traffic flows can often be effective in reducing localized concentrations of CO. In a nonattainment area with a NO_x problem, however, the same project could significantly increase vehicle speeds, thereby exacerbating ozone formation. The committee’s task was to examine the relative payoff of different strategies funded under the

program, recognizing that project rankings based on effectiveness and cost-effectiveness may differ by location.

The committee also distinguished between a retrospective and a prospective program evaluation. The consensus was that both were necessary to address the congressional request. Thus, the committee reviewed how the program has performed to date and attempted to summarize what could be gleaned about the track record of projects funded under the program. The committee also looked to the future and asked where the program should be headed in view of projected trends in air quality and congestion. That focus led to recommended changes in the program scope and emphasis to meet evolving needs.

The committee faced a number of challenges in conducting its evaluation. In this section, several of the key issues that affected the feasibility of what could be undertaken are raised, and their treatment by the committee is explained.

Evaluation of the CMAQ program is complicated by the program’s dual goals—air quality improvement and congestion mitigation. Given the legislative history of the program (following closely upon the CAAA of 1990), as well as its funding formula and regulations, which are focused heavily on the air quality objectives of the program, most would agree that CMAQ funds must be spent on projects that demonstrate some potential for improving air quality. The problem arises with the second goal—congestion mitigation. As noted, many believe this is a legitimate program goal and argue that projects that reduce congestion will also be beneficial for air quality. Others are less sanguine about such benefits. They believe many such projects, at least those that purport to lessen congestion by improving the efficiency of highway travel, would encourage new travel, thus reducing air quality benefits.

This divergence of opinion about the program’s fundamental goals (some label CMAQ the “split personality” program) makes it difficult to achieve consensus on how the performance of the program should be measured. In the spirit of ISTEA, which emphasizes local decision making, the federal program sponsors have not provided guidance on this topic. Rather, it has been left up to the states and local governments that identify, select, and program projects for CMAQ funding to determine how to balance these goals. Different metropolitan areas have differing objectives for how and why they spend CMAQ funds. Thus from a programmatic standpoint, it is difficult to compare outcomes across regions. The committee did not endeavor to resolve this ambiguity regarding program goals. Rather, the study was focused primarily on evaluating the effects of CMAQ-funded projects on what most agree is the primary program goal—pollution reduction.

Ideally, a comprehensive evaluation of the CMAQ program would include an attempt to quantify the effects of projects funded under the program on desired final outcomes—improved air quality and human health, and reduced congestion.¹¹ These outcomes should be measurable by such performance indicators as reductions in concentrations of criteria pollutants and numbers of pollution-related illnesses and deaths for the air quality improvement goal, and faster travel speeds and reductions in travel delay for the congestion relief goal.

In practice, however, the relatively small changes that result from CMAQ projects are difficult to measure. First, the outcomes are the result of a complex set of causal relations that presents measurement difficulties at every step. Second, the current state-of-the-art estimation process does not account for potential feedback effects. Figure 1-1 shows how emission reductions are estimated; outcomes for each CMAQ project change are estimated, and these become inputs for subsequent estimates of emission reduc-

tions and air quality improvements. In reality, the impact of any project is more complex. For example, trip reductions may reduce congestion, which in turn may result in more trips being made. Third, most CMAQ projects are small in scale and result in correspondingly small changes in travel behavior and emission levels. Fourth, these changes represent only a portion of a complex set of factors that affect ambient air quality levels and human health risks. For example, measuring the effects of a CMAQ project on reducing ozone, a key program concern, depends not only on the tailpipe emissions of the precursor pollutants, but also on the mix of NO_x and VOCs already in the local atmosphere, the transport of ozone or its precursors into the area, and local weather conditions (NRC 1991). Complex air quality models are used to relate reductions in precursor emissions to atmospheric concentrations of ozone, but such models are usually incapable of reliably predicting small changes in air quality that might be attributable to the typical CMAQ project, and indeed were not designed for this purpose. Thus significant uncertainty exists at every step of the impact estimation process.

Furthermore, CMAQ projects may have effects beyond those on air quality and congestion, which fall broadly into three categories: environmental, economic, and social. For example, environmental outcomes of CMAQ projects could include effects on ecosystems, as well as on levels of carbon dioxide (CO₂) and other greenhouse gases. Economic outcomes might encompass improved access and economic development. Social outcomes could include enhanced community liveability and quality of life and improved mobility for lower-income populations. Measuring these effects is difficult. With regard to ecological effects, for example, ground-level pollutants, whose sources are sometimes hundreds of miles distant, are known to alter the chemistry and composition of surface water and soils, as well as to affect sensitive plant and animal life (TRB 1997, 31–32). Identifying which types of CMAQ projects could have effects on ecosystems and the general nature of those effects may be possible, but the ability to pinpoint measurable effects of individual projects is unlikely. Many of the other outcomes of CMAQ projects, such as improved quality of life or more liveable communities, are general in

nature and lack well-developed performance measures, much less the data needed to quantify the effects. And even if the data were available, measuring such a long chain of impacts with a reasonable degree of confidence would be difficult because of the uncertainties involved at each step of the analysis and the small magnitude of the effects of any single project.

Other outcomes of the CMAQ program are apt to be more process-than goal-oriented. For example, the program’s broad scope and range of eligible activities may encourage greater involvement by nontraditional interests (e.g., air agencies, public interest groups, freight interests) in local transportation planning and decision making. The CMAQ program also provides a unique source of funds that can be used to support experimental, start-up projects and to leverage other funds in support of innovative transportation approaches to pollution reduction. These outcomes should also be taken into account, but they are difficult to verify and measure in any systematic way.

Because of these difficulties, the committee decided to limit its focus to the measurement of emission reductions in assessing the effects of CMAQ-funded projects on air quality and human health. Other outcomes were treated qualitatively to the extent that data were available for examining changes that may have been introduced by the CMAQ program.

The CMAQ program was never structured to provide for a comprehensive technical evaluation of the program at the national level. FHWA established a national database of all CMAQ-funded projects, and required program recipients to report annually on the funds obligated for each project and to estimate the emissions reduced for each affected pollutant. Presumably, the reporting requirement was intended to enable tracking of project results and progress. Consistent with the decentralized focus of the program, however, no provision was made for collecting the data in a uniform way so that projects could be compared across regions. Thus, the FHWA database proved insufficient for evaluating the effectiveness of CMAQ projects.

The changing context within which CMAQ operates also makes evaluation difficult, particularly with respect to how well the program addresses its primary goal of pollution reduction. Cars have become cleaner since the program was enacted in 1991, and they will continue to do so as new-vehicle emission standards are phased in and the fleet turns over. Some CMAQ projects, such as traffic flow improvements, that were implemented in the early program years, are likely to have shown greater emission reductions than they could yield today or in the future. Thus, what may be learned about the effectiveness and cost-effectiveness of past projects may not hold true in the future. Similarly, great progress has been made in many metropolitan areas toward addressing the pollutants that were of greatest concern when the program was enacted—CO and ozone—and that remain its primary focus. More progress could certainly be made in reducing these pollutants, but new concerns have arisen with emerging knowledge about the adverse health effects of particulates and air toxics, which have not been a program priority. This moving-target aspect of the CMAQ program makes it necessary to qualify the relevance of past program performance.

In light of the constraints detailed above, the committee adopted a broad-based approach to its charge. The committee’s approach included a review of existing related studies, an analysis of the CMAQ database, the commissioning of papers to obtain detailed analyses of two important topics, and the conduct of five case studies.

The committee was fortunate to be able to draw on several major studies related to its work. The NRC (2000) critique of the MOBILE model (the primary tool for emissions analysis), the National Cooperative Highway Research Program report on quantification of the benefits and costs of transportation control measures (NCHRP 2000), and the NRC (2001a) evaluation of the effectiveness of vehicle inspection and maintenance programs address many of the analytical and modeling limitations involved in quantifying the outcomes of CMAQ projects.

At least four other NRC reports were important for understanding the air quality problems addressed by the program—the NRC (1991) study on ozone and the more recent studies on airborne particulate matter (NRC 1998; NRC 1999; NRC 2001b). Finally, three other TRB reports were helpful in understanding the links among transportation, the environment, and congestion (TRB 1994; TRB 1995; TRB 1997). These reports, among others, provided the contextual information necessary to address Tasks A and B of the congressional request (evaluating the air quality impacts of emissions from motor vehicles and evaluating the negative effects of traffic congestion).

The committee commissioned an analysis of FHWA’s national CMAQ database (see Appendix C). This analysis was helpful in analyzing the general types of projects funded under the program and differences in spending priorities among geographic areas (Task C of the congressional request, determining the amount of funds obligated under the program and performing an analysis of the types of projects funded). The committee also examined the database as a potential source of information about project-level emission reductions and costs.

This study is not the first attempt to measure the effectiveness and cost-effectiveness of many of the types of projects now funded under the CMAQ program. Transportation control measures, in particular, have been part of urban transportation policy since the early 1970s (Meyer 1999, 575). The committee therefore commissioned a paper (included as Appendix E) to review the relevant literature, with a focus on more-recent studies and on available postimplementation studies aimed at determining the extent to which projected outcomes of CMAQ strategies (e.g., emission reductions) were realized (Tasks D, E, and F of the congressional request—evaluating emission reductions attributable to CMAQ projects, assessing the quantitative and qualitative benefits of the projects, and assessing the cost-effectiveness of projects with regard to congestion mitigation, respectively). In view of the inadequacies of the models and data on

which the results of many prior studies are based, the paper focuses on a small set of studies and strategies for which more in-depth and reliable data were available, as well as contextual information for interpreting the results.

The committee commissioned a second paper (included as Appendix F) to examine the cost-effectiveness of alternative strategies for controlling pollution, primarily from non-CMAQ-eligible mobile and point sources (Task G of the congressional request, comparing the costs of air pollutant reductions achieved under CMAQ with those achieved by other means). Recognizing the need for consistency between the two papers, the committee requested that the authors adopt similar approaches to such issues as level of aggregation for reporting emission reductions, related weighting factors, and treatment of costs. Both authors were charged with discussing the sources and extent of uncertainty for each class of strategy reviewed. Together, the two reviews provide a thorough scan of the relevant literature.

The committee conducted five case studies in selected metropolitan areas—Los Angeles, Chicago, Houston, Washington, D.C. (tristate area), and Albany—to gain better insight into how the CMAQ program operates in the field. The case studies helped the committee understand the many contexts in which the CMAQ program functions and the roles of different governmental agencies in implementing the program, including local views on program goals, strengths, weaknesses, and areas for improvement. Finally, the case studies helped the committee understand some of the difficult-to-measure qualitative aspects of the program (Task E of the congressional request, assessing the quantitative and qualitative benefits of CMAQ projects). To supplement the case studies, the committee heard briefings from local program administrators and other stakeholders at several of its meetings.

The items included in the congressional request are addressed in the remainder of this report. In Chapter 2, an overview of air quality and congestion problems, which provide the context for the CMAQ

program, is presented, along with a brief discussion of emerging trends that could affect the future direction of the program. Implications for program evaluation are considered. In Chapter 3 an overview of program operations to date is provided, including a review of funding allocations and eligible activities, a history of program spending trends by project category and geographic area, and a review of program operation in the case study sites. The committee’s assessment of the program’s results is given in Chapter 4. What is known about the cost-effectiveness of CMAQ projects is reviewed; the cost-effectiveness of alternative strategies for pollution reduction is examined; and the qualitative aspects of the program are addressed, drawing again on the case studies. The findings presented in Chapters 2 through 4 served as the basis for the committee’s summary findings and recommendations, which are presented in Chapter 5.

AASHTO American Association of State Highway and Transportation Officials

FHWA Federal Highway Administration

NCHRP National Cooperative Highway Research Program

NRC National Research Council

TRB Transportation Research Board

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