How long does it take to stop a train?

A somewhat educated guess would be around half a mile from that speed. Which to a freight engineer is phenomenal, we are used to needing double or triple that amount of room to stop form half that speed.

Curvature is another factor, tighter curves creating more flange bind and therefore more resistance. One other very important factor (in actuality the most important for any train) is grade. Ascending, stopping distance is shorter, while descending heavy grade adds the most significantly to stopping distance.

Like anything there are variables. How fast the track speed is for the area, passenger load, presence of moisture/liquids/ice on the rail, track gradient etc. Acela Express' acceleration tested out at about 1 mph/sec. before being put into revenue service.

It all depends on the length, weight, and speed. If you have an engine and a couple cars it can take a few hundred feet it moving slowly. A long frieght train (can be towards a mile long) can take well over a mile.

I've always heard that a train, moving at full speed, needs one to two miles to come to a complete stop.