Chattanooga Times Free Press

It's still not clear what caused the bridge's concrete railing to come crashing down, according to Tennessee Department of Transportation officials. However, they are confident the bridge, which was built in the 1950s, is structurally sound and its condition will not lead to further injuries.
...
The bridge was inspected in the middle of last year and its overall condition rating found to be fair, TDOT records show.
...
Officials are reviewing video footage and weigh station records to see if an oversized truck may have caused the bridge's damage.

Very scary. Amazing that only one person was hurt when they drove into the fallen debris.

Tennessee Structurally Deficient Bridges

-There are 616,087 bridges in America
-Of those, 47,052 (nearly 8%) are "structurally deficient" and need urgent repairs
-235,020 bridges (38%) need some sort of repair
-Americans cross structurally deficient bridges 178 million times a day, including such landmarks as the Brooklyn Bridge and the San Mateo-Hayward Bridge over the San Francisco Bay
-The average age of a structurally deficient bridge is 62 years

At our current pace it'll take 80 years to repair all the structurally deficient bridges in the US, a report finds

I wonder if recent earthquake activity affected the integrity of the brudge?