The General Accounting Office (GAO) examined the development and application of intelligent vehicle and highway systems (IVHS), more commonly known as smart highways, as a means of reducing traffic congestion. The following questions were addressed: What have the major studies concluded about the potential effects of IVHS, and to what extent are these findings empirically based? What additional information can be learned from IVHS field tests under way? What major obstacles could impede the realization of transportation benefits possible through IVHS technologies? In brief, GAO found that the empirical basis for judging the effects of IVHS is limited but nonetheless positive and promising.