This is a very simple car made of three objects, a body mesh, a single wheel mesh, and a rigid body.
The car uses local2parent to mimic the movements of a car by rotating the car about the rear axle position. I also equipped it with a simple waypoint system that reads from an array and spawn the cars randomly along the path. This can be used for simple traffic cars in for example an open world game like GTA or a racing game with many opponents. It's not very cpu hungry as it doesnt use any of the car or wheel objects. I think it can be optimized even more if the imposter wheel and body meshes is used for all the cars in the scene. I was able to run 21 cars at a decent framerate.
Big thanks to Bobby Soon/Chronocide for the help with waypoint navigation:)
It's free for non-commercial purposes if anyone wants to use it, just remember to mention me & cronocide in the credits
The car uses local2parent to mimic the movements of a car by rotating the car about the rear axle position. I also equipped it with a simple waypoint system that reads from an array and spawn the cars randomly along the path. This can be used for simple traffic cars in for example an open world game like GTA or a racing game with many opponents. It's not very cpu hungry as it doesnt use any of the car or wheel objects. I think it can be optimized even more if the imposter wheel and body meshes is used for all the cars in the scene. I was able to run 21 cars at a decent framerate.
Big thanks to Bobby Soon/Chronocide for the help with waypoint navigation:)
It's free for non-commercial purposes if anyone wants to use it, just remember to mention me & cronocide in the credits
SimpleAIcar.3dr
I tried to use rb imposters but I could not get the custom L2P function to work with an imposter as both parent and child, so I think you'll need a separate rb for each car. 
, anyway I moved my driving sim project to unity so I don't have much time left to experiment with this, but I gotta say it was a very useful experience and made scripting in unity very easy to adapt to. I pretty much did a remake of this waypoint system thing in Unity.