It could be, but being near a railroad (or highway for that matter, or even on a busy street) definitely reduces its value. Can you find any comps nearby the railroad too? Those would be the best to use. If not, just make sure to be very conservative about what selling price it could go for. It's going to be at the lowest end (and maybe a bit lower) of the comps available.
Also visiting the house, even if you just sit out front in your car can help you decide how bad the noise is. Then from there you can decide how much of a detriment it will really be to renting the place.