Tomlinson, specifically both rollers are supplying power to the engine full time and have no relation to what direction the engine is traveling. Actually the main purpose of having two sets of rollers is to bridge gaps where there is no power so the engine will keep going. It is possible on some switches (crossovers) for both rollers to be on a dead spot however. This problem has lessened by some more expensive engines having two double rollers, i.e. there are four rollers on the track.
Dennis
