People choose suicide methods that are consistent with previous life trauma. People who choose to be hit by a train in particular are correlated with physical punishments, either from parents and caregivers, or from others. I read of a case study where a man who was captured in war was tortured by being beaten by a group of soldiers, and he chose to end his life by train. So it's not always childhood trauma that does it.

It makes sense, because our brains categorize memories by emotion (much like how a library sorts books by author). Being suicidal is a highly distressed state, especially directly beforehand. A lot of times people cannot access happier or more emotionally distant memories when in an emotional state. So if you are extremely distressed, you'll be remembering your worst moments. When planning your own suicide, you'll be remembering all the worst moments while trying to plan. Those memories leak into the present and affect present day decisions.