It's not the pull that leads to problems. It's the braking. The engines in front might have come to a full stop before the last cars a mile or more back have ev

It's not the pull that leads to problems. It's the braking. The engines in front might have come to a full stop before the last cars a mile or more back have even gotten the message that they need to decelerate. Do that on a curve going down a hill and the cars in motion just keep going, usually into a river or some buildings beside the tracks. The longer the train, the more the whip cracks.