Only a relatively small proportion is financed through public or private borrowing or private (equity) investment. The federal government supports surface transportation infrastructure financing mainly by providing a tax preference for bonds issued by state and local governments. Other mechanisms include federal loan programs, such as the Transportation Infrastructure Finance and Innovation Act (TIFIA) program, which can help leverage private investment via public-private partnerships (P3s), and federally authorized state infrastructure banks (SIBs). Nevertheless, none are as costly as federal grant funding. This is because project financing relies more heavily on revenue streams created at the state or local level in order to repay loans or provide a return to private investors. In many cases, revenue to finance a project has been provided by a highway or bridge toll, but it could be, among other possibilities, a pledge of future sales tax or real estate tax revenues. This report outlines current federal programs that support the financing of surface transportation infrastructure investment and the relative impact these have on the federal budget. It goes on to discuss legislative options for modifying the federal role, including provisions related to tax credit bonds, dedicated federal funding for SIBs, and the creation of a national infrastructure bank. Local government provided the most support, followed by passenger fares and other operating income, state government, and the federal government ( Table 3 ). Financing is normally not arranged at the federal level, as the federal government builds few transportation projects directly. P3s and private investment in surface transportation are relatively larger in many other countries, including Portugal, Spain, and Australia. The "public" in public-private partnerships typically refers to a state government, local government, or transit agency. Probably the main way in which the federal government has encouraged P3s and private financing in transportation is through the TIFIA program that provides long-term, low-interest loans and other types of credit to project sponsors. 114-94 ) authorized the creation of a new bureau within DOT to consolidate federal transportation financing programs and support for P3s. Railroad Rehabilitation and Improvement Financing (RRIF) Program

Under RRIF (45 U.S.C. State Infrastructure Banks

Another source of financing for surface transportation projects is state infrastructure banks (SIBs). Funding source .
Investment in surface transportation infrastructure is funded mainly with current receipts from taxes, tolls, and fares, but it is financed by public-sector borrowing and, in some cases, private borrowing and private equity investment. Financing is normally not arranged at the federal level, as the federal government builds few transportation projects directly. This report discusses current federal programs that support the use of debt finance and private investment to build and rebuild highways and public transportation. It also considers legislative options intended to encourage greater infrastructure financing in the future.
The federal government's largest source of support for surface transportation infrastructure is the Highway Trust Fund (HTF), which is funded principally by taxes on gasoline and diesel fuel. Funds from the HTF are distributed to state governments and local transit agencies for projects meeting federal standards. State governments, local governments, and transit agencies must also contribute their own resources because grants from the HTF do not meet states' entire surface transportation capital needs. The federal government supports additional infrastructure spending by providing a tax exclusion for owners of municipal bonds, or "munis," issued by state and local governments. The federal government also supports project finance through loan programs, such as the Transportation Infrastructure Finance and Innovation Act (TIFIA) program and the Railroad Rehabilitation and Improvement Financing (RRIF) program, which can help leverage private investment via public-private partnerships (P3s), and through federally authorized state infrastructure banks (SIBs).
All of these financing mechanisms impact the federal budget, although none are as costly as federal grant funding. With less federal support, financing places a greater burden on state and local governments to identify revenue sources to repay loans or to provide a return to private investors. In many cases, nonfederal revenue to finance a project is provided by a highway or bridge toll, but it could be a pledge of future sales tax or real estate tax revenue.
There are many legislative options that Congress might consider in modifying the federal role in surface transportation financing. This report considers five:
1. Creation of a new type of bond offering federal tax credits to investors in infrastructure. 2. Changes to the TIFIA and RRIF programs. 3. Greater encouragement for P3s. 4. Creation of a national infrastructure bank to provide low-cost, long-term loans for infrastructure on flexible terms. 5. Enhancement of SIBs that already exist in many states, possibly with dedicated federal funding.