Trigger warning/graphic answer.
Something like F=ma likely applies. A heavier/higher mass train may inflict greater injuries, but its far from the only factor and is not what determines instant death.
Therefore, fair warning, death is not even guaranteed, not necessarily instant and injuries are likely to be horrific. Amputations, fractures, skin tearing and melting, maybe worse. Not to mention the emotional trauma inflicted on the driver and anyone that has to witness the aftermath.
I'm sorry you're feeling this way.