How do I make sure I will get killed by an incoming Train

[Lenmenhen]

How fast should a train go in order to kill me?How should I jump in order for it to kill me swiftly and painlessly?I don't want to survive the attempt if I'm going to try it in the future.

 

[vexi]

I think the best chance of a quick and painless death is laying down, neck on the rails and legs tight to your chest.
And most modern trains will cut off your head on impact.

I don't recommend jumping in front of a train, because there is a chance of survival. Or not immediate death, but it will be painful.
If you're not sensitive to gore I recommend taking a look at cases of people dying and surviving from train accidents. It helped me to decide if this method was for me.