There was explanation for that in one scene,because if they would have broke the coupling at that speed the train would derail and every passenger will die.
I wish they had konkan route at that time so that they would divert it there,and eventually fuel runs out and train stops.
Take another one
If the train had LHB coaches,they would have send the message...
more... to the passengers by the help of all India radio to tie themselves to some object,so that they can derail it at any station safely.
But then again the movie won't be made with that story.