There's another entry for "train bumper" but that is actualy a car far ahead of the main one hoping to detect obstacles, and only acts to reduce the chance of a collision. This may be impractical in many cases, and collisions will happen anyway. So why not have an extra car *in front* of the engine car that simply absorbs some of the force of a collision? You could also have a rear one behind each train. This would have helped a lot in the recent DC and Los Angeles collisions--they still would have happened, but lives could have been saved with it.

Because you don't want to compromise visibility, the extra car can be low to the ground, maybe only 1/2 the normal car height. Design it specifically to break into fragments upon impact to absorb some of the collision force; maybe a carbon fiber frame with some plastic or foam inside to absorb kinetic energy.
-- scottinmn, Jun 25 2009

random, halfbakery