11-25-2009, 03:37 PM
You are right about friction of the wheels on the rail being the limiting factor for stopping. Regarding dynamic brakes, I don't think they are used for stopping except in an emergency situation where the engineer is trying anything to get it stopped. Primarily they are used to hold a train's speed down going down a grade. The problem with friction brakes is that if they get to hot, they will fade and stop working. Dynamic brakes don't have that problem, but I remember a wreck on Cajon Pass back before the mergers of the U.P. and S.P. or B.N. & S.F. The train was coming down grade toward San Bernardino when the resister bank of one locomotive blew up. The train ran away and crashed, I don't remember if it was a Santa Fe or S.P.