When I was a kid, messing around with CO2 cartridges for use in rocket propulsion was strictly verboten. I had a friend who proved the caution a worthy one when he blew off part of a finger trying to stuff ground match heads into an empty cartridge.
But as with many things that are dangerous, C02 propulsion can be made relatively safe with adults in the room who know what they’re doing. In this project video from The Q, they show how they made rocket cars, a race track, and a rocket car firing mechanism.
There are some problems here. The bottle cap wheels, while clever, don’t do much for the smooth travel of the vehicles and the angled carts on the vehicles (especially the heavier, dual-cart truck) doom them to a front-lifting, unstable trajectory. That said, it would be undeniably fun to build a track like this and experiment with tweaking all of the variables until you got consistently stable results.