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The Congestion Mitigation and Air Quality Improvement (CMAQ) program was enacted as part of the surface transportation legislation authorized in 1991 to provide support for projects that would aid local efforts to meet the strict new federal deadlines imposed by the Clean Air Act Amendments (CAAA) of 1990. CMAQ was included in the reauthorization of surface transportation legislation in 1998 for another 6 years, and funding for this period was set at $8.1 billion. In the 1998 legislation, Congress also requested an evaluation of the effectiveness of the program and the cost-effectiveness of the projects funded by the program.
CMAQ funds are focused primarily on the transportation control measures (TCMs) contained in the 1990 CAAA (with the exception of vehicle scrappage programs, which have not been permitted). TCMs are strategies whose primary purpose is to lessen the pollutants emitted by motor vehicles by decreasing highway travel (for example, bicycle, pedestrian, and some transit projects) and to encourage more efficient facility use (for example, projects focused on ridesharing and on traffic flow improvements, such as signal timing). In addition, CMAQ funds may be used for projects that reduce vehicle emissions directly, such as through vehicle inspection and maintenance programs and purchase of alternative-fueled transit vehicles. In the spirit of the legislation that originally authorized the program, decisions about project selection are made at the local level, usually by or through the local metropolitan planning organization.
After reviewing the limited information available about these types of projects, the committee that evaluated the CMAQ program concluded that, when compared on the sole criterion of tons of emissions reduced per dollar spent, strategies aimed directly at emissions reductions such as emissions and fuel standards for new vehicles, well-structured inspection and maintenance programs, and vehicle scrappage programs are more cost-effective than the typical CMAQ TCMs, which tend to depend on changes in behavior. A few behaviorally based TCMs, however, such as pricing and regional ridesharing, compare favorably with vehicle- and fuel-based strategies. The committee recommended that the CMAQ program be continued, in part because it is a "funded" rather than an "unfunded" mandate. The committee also called for a focus of future projects on reductions in emissions with the largest public health consequences and for improved evaluation of project effectiveness.