Summary: 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.
