This CRS report, updated July 2008, discusses highway bridges. "The sudden failure and collapse of the I-35W Interstate System bridge in Minneapolis has raised policy concerns in Congress regarding the condition of the nation's transportation infrastructure in general, and in particular the federal role in funding, building, maintaining, and ensuring the safety of roads and especially bridges in the United States. The National Transportation Safety Board (NTSB) expects to determine probable cause of the collapse by the end of 2008. An interim NTSB finding implicated a flaw in the original bridge design as a contributing factor. Of the 600,000 public road bridges listed in the National Bridge Inventory, roughly 12%, or 72,000, were classified as structurally deficient as of 2007. This is, however, roughly half the number classified as deficient in 1990. Given the I-35W collapse, however, even this lower number of deficient bridges leaves Americans potentially exposed to what some might consider an unacceptable level of risk. [...]. At current annual spending levels, roughly $10.5 billion (2004 dollars at all levels of government), the bridge investment backlog (in dollar terms) would be reduced by roughly half by 2024. Reducing the backlog to near zero during the same period would require an estimated annual spending rate of roughly $12.4 billion (in 2004 dollars). The Emergency Relief Program (ER), administered by the Federal Highway Administration (FHWA), provides funding for bridges damaged in natural disasters or by catastrophic failures. The program provides funds for emergency repairs immediately after the failure to restore essential traffic, as well as for longer-term permanent repairs."
CRS Report for Congress, RL34127