I expect it would be more able to cleanly cut through the bodies or throw them out of the way with more momentum. If it’s going slow it’s more likely to ride up on top of a body. Anecdotally, I’ve heard that derailers tend not to work on fast moving trains.
But isn’t it more likely to derail if it gains momentum?
Depends
Not if the track is perfectly straight.
There are People lying on it, so it’s probably pretty uneven and bumpy, no?
I expect it would be more able to cleanly cut through the bodies or throw them out of the way with more momentum. If it’s going slow it’s more likely to ride up on top of a body. Anecdotally, I’ve heard that derailers tend not to work on fast moving trains.