(Newser) – Think about this the next time you drive over a bridge: An AP analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified as "structurally deficient" and 20,808 as "fracture critical." A bridge is deemed fracture critical when it doesn't have redundant protections and is at risk of collapse if a single, vital component fails; it's structurally deficient when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.

Of those, 7,795 were both structurally deficient and fracture critical—a combination of red flags that experts say indicate significant disrepair and similar risk of collapse. The AP looked at those bridges, which carry more than 29 million drivers a day. They're located in all 50 states (among them: New York's Brooklyn Bridge) and many were built more than 60 years ago. Cities and states would like to replace the aging and vulnerable bridges, but few have the money; nationally, it is a multibillion-dollar problem. Of course, engineers and officials say the bridges are safe, but the Interstate 5 bridge in Washington state that collapsed in May was fracture critical and the Minneapolis bridge that collapsed in 2007 was structurally deficient. Click for more. (Read more bridge stories.)

