Stabilizing the bridge - spoiler alert

Not that we really expect everything in movies to make sense, but this idea that first Bill, and then Jack have of possibly stabilizing the bridge by driving a loaded train onto it doesn't make much sense to me. I understand that they were both trying to find an acceptable way to commit suicide, but the likely result is exactly what happened, losing the bridge and losing a train plus a bunch of flat cars. Which has to cost their employer a lot of extra money. So if the bridge is likely to go anyway, why risk the added cost. Both are supposed to be nobly motivated, so why screw the railroad? Why not just step in front of a moving train? Jack nearly does that at the end, but survives to take out the bridge.