This would only work in a heavily scripted mini game with vehicles made strictly for this.
ever looked at the show health bar mod? Or at the cloak and Dagger script?
You can just use the energy bar:
when somebody enters a vehicle, the energy bar should be showed and when the player moves, it should drain energy (slower than the Cloak and Dagger :D)
when the energy bar is empty, you can't move your vehicle anymore.
When somebody leaves a vehicle, the energy bar should disappear
easy script :D
