Physics tells us that we should accelerate to spend the least amount of time in the danger zone (rail bed). Since the velocities are orthogonal, it doesn't matter if you are hit by a train when your car is going 55 or 5 MPH (probably, unless trees in the resulting vector of your now pulped car).

It never made any sense to me to see school busses stopping at a grade crossing, then taking an extraordinarily long time to cross those tracks. What happens if the engine fails while on those tracks and a high speed train appears.

No, my vote is to make sure you have a clear view of the tracks in both directions and punch it. Less probability of interacting with a train.