Summary: The diversity of transportation programs, problems, and policy issues and their changing nature influences the scope and direction of GAO plans for auditing Federal transportation programs. A staff study was made based on a current assessment of the major factors affecting the economic viability and efficiency of U.S. transportation systems. It discussed selected major issues which GAO audit work must address and summarized related audit work discussing long-range trends in energy, the environment, and new technology which will affect transportation in the future. The most difficult transportation problems frequently affect several transportation modes and involve the interaction among transportation modes. In its study, GAO addressed: (1) the control of mass transit costs and increasing transit revenues; (2) assuring adequate rail service for the Northeast and Midwest; (3) the effectiveness of Federal traffic safety programs; (4) the effectiveness of programs for fuel economy and consumer protection for automobile owners; (5) the impact of deregulation of truck, rail, and household goods moving industries on shippers and consumers; (6) Federal responsibilities for the national aviation system; (7) the cost and need for rail passenger service; and (8) cost-effective ways to revitalize the U.S. merchant marine and shipbuilding industries. In the light of Administration proposals to reduce Federal spending in the transportation areas and cutback regulations, congressional needs and interests are shifting rapidly in the area of transportation. The outcome of the congressional actions on the Administration's proposals will not be clear for some time but could result in substantial shifts in the nature and focus of GAO audit work in transportation.