Urban Transportation

Reducing Vehicle Emissions With Transportation Control Measures Gao ID: RCED-93-169 August 3, 1993

Motor vehicles are the main source of air pollution in many cities. Excessive levels of ozone and carbon monoxide in these areas have been linked to a variety of illnesses, including lung and heart disease. This report examines the use of transportation control measures (TCMs) by states and localities to control vehicle emissions. TCMs range from traditional approaches, such as improving commuter train service and promoting employer-provided carpooling, to economic measures, such as imposing gas taxes and emission fees. GAO concludes that although TCMs should cut overall emissions by less than five percent, they can complement other programs designed to address pollution problems in areas that have not met federal air quality standards. Moreover, the additional reductions in emissions resulting from traditional TCM programs may help localities meet the standards mandated in the Clean Air Act Amendments of 1990. Pricing measures would be more effective in reducing air pollution but would also encounter greater opposition because of their direct costs to the traveling public. Regardless of the kinds of TCMs that states and localities implement, more research on their effectiveness is clearly needed.

GAO found that: (1) although traditional TCM are projected to reduce overall emissions by only 5 percent, transportation planners believe that TCM, in conjunction with other pollution reduction programs could help localities achieve greater reductions in air pollution and meet pollution legislation requirements; (2) 56 percent of metropolitan planning organizations stated that TCM would receive strong emphasis in their transportation programs over the next 5 years; (3) market-based TCM that create financial disincentives and attempt to change travel behavior may be more effective than traditional TCM in reducing automobile and carbon monoxide emissions; (4) although the Department of Transportation and the Environmental Protection Agency (EPA) are encouraging states to implement more market-based TCM, such as gasoline taxes or emissions fees, these measures are often costly and economically and politically unpopular; (5) localities that cannot obtain support for market-based TCM can maximize the benefits from traditional TCM by focusing on specific congested corridors and implementing TCM that reduce the number of trips and miles traveled; and (6) more TCM research is needed to determine its overall effectiveness, update literature that is outdated, and help justify future market-based measures.


Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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