The fact that the bridge collapsed isn't that surprising. The fact that more bridges don't collapse with the abysmal state our infrastructure is in is surprising. Still, there's something that just feels weird about seeing a bridge that's broken.
The results of it's last inspection on the National Bridges registry can be viewed here. It was built in 1955, rated as acceptable but was considered functionally obsolete as of 2000. As of the last inspection in 2010 the bridge had a structural rating of 5 out of 9 which gives it a "Somewhat better than minimum adequacy" rating.