This is merely a thought, and I haven't checked the FRA regs. in regards to this:

Considering the weight of the railcars vs. an 175lb person on a 20 pound bike, what prevents a strip of rubber - hard enough to remain rigid under a bicycle and its rider, but soft enough to deflect from the wheel flange of a 50 ton railcar - from being inserted in any gap that doesn't contain switch points?

-Kurt