Traffic congestion on the nation's highways and streets continues to increase and affect mobility, energy conservation, and air quality. GAO evaluated federal efforts to encourage better management of the nation's highways through the use of low-cost transportation systems management techniques. Overall, GAO found that the federal government plays an important role in facilitating the local implementation of such techniques to reduce congestion and improve air quality. This role includes funding assistance, planning requirements, and technical support. These current efforts have not, however, been fully successful in achieving widespread transportation systems management--and particularly transportation demand management--usage. GAO found that: (1) TSM encompasses low-cost techniques for improving the efficiency of surface transportation, including supply management techniques, which include traffic signal coordination and ramp metering, and transportation demand management techniques, which include carpooling and vanpooling; (2) federal efforts to achieve widespread TSM usage have not been fully successful; (3) over the last decade, the actual total expenditures for TSM with federal aid has remained small relative to total allocations; (4) although the federal government has sought to promote better supply and demand management by including certain TSM projects under an incentive provision that included other operational improvements, the provision has not significantly influenced the amount of TSM implemented; (5) transportation planning requirements alone appear to be insufficient to guarantee that TSM and transportation demand management are implemented, due to local reluctance to fully embrace transportation demand management and an uncertain connection between transportation planning and any consequent project funding; (6) federal policy could further support innovative strategies to better manage traffic demand through ongoing technical assistance; and (7) due to 1990 Clean Air Act requirements, the need for technical assistance could increase greatly.