Passenger and freight traffic are expected to grow substantially in the future, generating additional congestion and requiring continued investment in the nation's surface transportation system. Over the past 12 years, the federal government has provided hundreds of billions of dollars for investment in surface transportation projects through the Intermodal Surface Transportation Efficiency Act of 1991 and its successor legislation, the Transportation Equity Act for the 21st Century. Reauthorization of this legislation is expected to provide hundreds of billions of dollars more in federal funding for surface transportation projects. For this investment to have the greatest positive effect, agencies at all levels of government need to select investments that yield the greatest benefits for a given level of cost. This report provides information about the processes that state and regional transportation decisionmakers use to analyze and select transportation infrastructure investments. GAO identified (1) key federal requirements for planning and deciding on such investments, (2) how benefit-cost analysis facilitates sound decisionmaking, and (3) other factors that decision-makers consider in evaluating and deciding on investments.