Many states, cities, and localities are building or planning mass transit projects to meet the nation's transportation needs. The New Starts program, administered by the U.S. Department of Transportation's (DOT) Federal Transit Administration (FTA), is an important source of new capital investment in mass transportation, providing grants to project sponsors (e.g., state and local government authorities), for the construction of major transit facilities. FTA uses contractors, known as project management oversight contractors (PMOC) and financial management oversight contractors (FMOC), to help oversee the planning, construction, and financing of major capital projects, including those funded under the New Starts program. This report, as mandated by law, discusses (1) how FTA uses PMOCs and FMOCs to oversee New Starts projects and how the agency procures, monitors, and evaluates the contractors' services; and (2) the benefits of FTA's oversight approach and the challenges FTA faces in conducting its oversight. GAO reviewed applicable statutes, FTA guidance, regulations, and budget data, and interviewed DOT officials, project sponsors, contractors, and industry stakeholders. GAO is not making any recommendations in this report.