move a car around a curved track at variable speed

I need to move a car around a curved track and would like to be able to adjust the speed. What is the best way to do something like this?

Check out the car tutorial in the resources section. It really helped me. You can set up your own car, and there is a prebuilt one so if you like you can just use that. If you don't want to do that, use a script to apply a torque, and then perhaps the vertical keys to adjust the tourque.

There is another car tutorial with a simple but effective waypoint system on the net:

Andrew Gotow’s Unity3D Car Tutorial