A great infinite runner, but the link to the theme feels a little bit weak. I actually think that it would be fun to tone done the speed, and have one person control both cars in the multiplayer mode.
My only real qualm is that the hitboxes for obstacles feel a little bit too big. They're probably accurate, but I'd recommend making them (or the car hitbox) slightly smaller, so it doesn't feel unfair when you graze the edge of a barrel and then lose.