Bridge Collapse

The bridge collapse in Minneapolis is a horrible calamity.
As I was watching the TV coverage of the collapse and the questions about its cause: construction work, age, terrorism, I thought of the times when I have been on the Kansas Expressway Bridge over James River Freeway waiting for the light to turn green so I could head east on James River. There have been times I could have sworn I felt that bridge shake.

I remember somewhere reading that bridges were designed to "float" due to variations in ground temperature, water density, freeze and thaw cycles.
I wonder if the compression of traffic into two lanes, the bumper to bumper traffic and the vibrations caused by the cars and trucks hastened the collapse of the bridge.