Freight cars are not the optimal crash absorbers, particularly flat cars which have the greatest potential to concentrate the impact forces on the drawbar, transmitting them exactly where we are most concerned about lack of structural strength. And then maybe pop sideways, or ride up over the drawbar and slice along the car frame.
A carbody that spreads the impact forces and absorbs them, and perhaps crumples in just the right way, would be optimal. But instead of looking for a freight car that has those structural characteristics, a matchng passsenger coach works extremely well.... and the riding characteristics, as noted, are better matched to the desired speed and braking. And the couplers are most compatible.
- Paul