Some people survive but it really depends on how you approach it. If you just throw yourself underneath a slow train then there's a chance you will survive with awful injuries. Lots of people who fail this method do not plan it and just do it out of desperation.
There was a guy on here that told me on my train thread that he'd never do it because he'd not want others to see, but he travelled to a station to access a bridge to jump off, but there was an anti-ctb barrier there stopping him, and he ended up doing the train method anyway as it was the only option left to him at the time.
His user name was notforlong, see his posts here -...