Hi. Sorry you've been brought to that point.
Is there no other option available for you other than the train if I may ask?
From what I've read it has a high fatality rate if it strikes you at high speed, Not when it's slowing down to the platform. That case you might die but it might not be as quick or painless, or you might survive in which case you definetly won't be in a painless state, maybe for a while before you eventually die. Just that to consider in the execution. I guess you have taken in consideration too that the train wouldn't be able to slow down or stop if it sees you laying there. Don't know your plan details.
The method is okayish with mortality, but my main gripe with it is the trauma it causes on the driver and potential witnesses. It is very gory. And a lot do report that trauma after witnessing it. I'd advise for other methods honestly but that's me.
Sorry if all that might affect your fear or SI about it, it's just some info I think you should know if that's your method. You may already do in that case I'm sorry.
As for beating SI, depends on the details of your plan. Don't know where or for how long you'd be laying. You could close your eyes and listen to music so as to not hear it approaching... It's just not easy by the nature of it you are right. It's a scary big and fast metal thing after all.
I honestly wished you didn't have to do that, it's up to you in the end. The info is there. If you ever want to talk, share or just vent anything you can do that here too, whatever may help or make it just a lil easier these days. Lots of hugs <3