Not sure if this is the right spot to post this, just today I spawned in a new position in the Biodome (at least I haven't spawned there before). It seems like a good spot, though when I was dropped in place I instantly started rolling down the hill. Maybe you could tweak where the car spawns or have the brakes on automatically when spawning to avoid this. I've also noticed in races the car sometimes slides forwards or even sideways slightly while the countdown is showing.
Though just after I noticed an AI spawn here and they didn't roll down, just stayed still until the countdown finished.