From the summary:
From 2008 to 2011, governmental spending on surface transportation infrastructure–highways, mass transit, and passenger rail–totaled $200 billion a year. The federal government spent more than $50 billion a year–mostly in the form of grants to state and local entities, which then determined what projects to fund–and state and local governments spent more than $150 billion a year of their own funds.
If future government spending on surface transportation infrastructure matched those recent amounts, however, the condition of the highway and transit systems would probably deteriorate. To increase the funding available for infrastructure projects and to improve the selection process for those projects, some analysts and policymakers have suggested the creation of an “infrastructure bank.” In this report, CBO analyzes an illustrative federal infrastructure bank for transportation–one that is representative of those in many recent proposals.