For those of you who can understand such engineering terms, I found a link from the Corp of Engineers with specs for the Mississippi River system. On page 104 (in my Adobe browser) it shows the I35 Bridge information in St. Paul. Maybe one of your engineering type of people can explain all of this in layman’s terms.
http://www.navcen.uscg.gov/pubs/LightLists/V5COMPLETE.pdf
Here in Minnesota, the temperature can drop down to -40F in the winter and over +100F in the summer. This temperature change does place a horrible strain upon the structures in the State. Having a highway suddenly buckle and thrust upward almost six inches, has happened rather frequently in the summer.
This was an old bridge, and the temperature changes finally caused something in it's basic structure to fail.
But what the heck, we have a new choo-choo train!
Span: The length of the longest section of bridge over the river is 390 feet.
Vertical: The bottom of the bridge is 60.1 feet above the normal level of the river so a 60 foot tall boat can pass under it. The river is dammed up to keep it deep enough for barge traffic. The “Normal Pool Elevation” is the usual level of the water upstream of the dam.