Nice. Now just if you could make it more physics'y. As in, make it go faster when it falls downwards and make it look like it is putting in extra effort, in cases it is going upwards, higher than what momentum would take it.
If you feel like doing this, I'd suggest using parameters for:
gravity
momentum
friction, so just reduce momentum based on traveled distance
minimum speed, to make sure it keeps going and that will look like it is using its motors to keep running
Also my immediate thought is that the End of the track when it connects to the Start isnt doing it with derivatives and therefore looks not smooth/shockfree.