Bridge Out

On the way to (and from) Colorado, I encountered the bane of my highway existance: lane closed ahead. Some lane closures are alright, such as left lane closed. Right lane closed means I have to change lanes, which is more work than I like to do out on the road. This particular lane closure was a left lane, and a very short one - just around a single overpass. The eastbound lanes under the overpass were taken up by the most sturdy scaffolding I had ever seen. It looked like railroad ties nailed together. And there wasn't any construction equipment around either, as if someone had just built this structure and then forgotten about it. I wanted to stop and shoot some pictures, but it's bad luck to stop on the highway unless absolutely necessary.

Reading Snopes today revealed the story of how this came to be (with pictures):

A hoe weighing 8 tons is on top of a flatbed trailer and heading east on Interstate 70 near Hays, Kansas. The extended shovel arm is made of hardened refined steel and the approaching overpass is made of commercial-grade concrete, reinforced with 1 1/2 inch steel rebar spaced at 6 inch intervals in a criss-cross pattern layered at 1 foot vertical spacing.

Solve: When the shovel arm hits the overpass, how fast do you have to be going to slice the bridge in half? (Assume no effect for headwind and no braking by the driver.)

Extra Credit: Solve for the time and distance required for the entire rig to come to a complete stop after hitting the overpass at the speed calculated above.