Steve I have enough knowledge about electrical to be dangerous and I have not heard arc shoots in twenty years. I will try to answer your questions about that since you have waded into the area of serious circuit breakers.
A couple of simple observations. No such thing as an instantaneous breaker. The breaker has two pieces of metal and when bad things happen they open. There is always an arc between the contacts until they are far enough apart. In large heavy duty breakers it takes a serious gap for the arc to stop. Hence the need for shoots. I would guess a minor factor in train applications.
Back to your original questions go back to Pat and John, speed and the curves on time.
Back feed well we have had cases when motors turned into generators and that wreaked havoc but not a concern with train motors.
