How does the Secret Service protect Obama on his rail trips?

Obama seems to be taking the train. My question is how do they protect against a planned derailment? Do they walk the entire track or what? It seems like a lot of miles to cover to prevent someone from putting a bomb on it and trying to derail the train.

A Hi Rail Truck, maybe?

That was my first guess too but a train cant exactly stop on a dim and nothing is stopping from some guy hiding in the bushes waiting for the train to come and run out and put a bomb on the tracks. I have to assume that their are some kind of aircraft flying around the area with IR sensors like police use to find people in the thick. Would this be a reasonable assumption?

Handcar?

CNN was discussing this earlier today, complete with 3D diagrams of the moving “tunnel of safety” established by the military, including helicopters overhead, ground forces on the roads nearby, and Coast Guard ships on the rivers.

It wasn’t nearly as fascinating as I’ve made it sound.