TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 513: Evolving Debt Finance Practices for Surface Transportation explores a variety of debt mechanisms and tools to finance transportation infrastructure investment. The amount of debt and frequency of issuance vary substantially across states. In most states, provisions included in constitutions or statutes (or combinations of the two) govern the level and form of debt issuance. As well, many states have formal policies that govern debt issuance and management. The study documents new developments in flexible finance tools, including those offered by the federal government.