Federal funding for highways is provided to the states mostly through a series of grant programs known as the Federal-Aid Highway Program, administered by the Department of Transportation's (DOT) Federal Highway Administration (FHWA). In 2005, the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) authorized $197.5 billion for the Federal-Aid Highway Program for fiscal years 2005 through 2009. The program operates on a "user pay" system, wherein users contribute to the Highway Trust Fund through fuel taxes and other fees. The distribution of funding among the states has been a contentious issue. States that receive less than highway users contribute are known as "donor" states and states that receive more than users contribute are known as "donee" states. GAO was asked to examine for the SAFETEA-LU period (1) how contributions to the Highway Trust Fund compared with the funding states received, (2) what provisions were used to address rate-of-return issues across states, and (3) what additional factors affect the relationship between contributions to the Highway Trust Fund and the funding states receive. To conduct this review, GAO obtained and analyzed data from FHWA, reviewed FHWA and other reports, and interviewed FHWA and DOT officials.