5 mph would have been way way too fast. Are you sure you weren't thinking in km/h? On most US RR, 3 mph is the absolute maximum allowed, and the target speed is between 1 and 1.5. Bashing the cars together, even if it doesn't cause a derailment, can damage the equipment. PS: Save.
Well according to the tutorial the maximum speed for the F7 switching is infact 5mph although it doesn't make much sense I came in with a different set of cars at like 8mph didn't derail also I did save but it doesn't seem to do update at all because I did it twice only saved the first one and ignored the second one