If you have a looping track, then it stands to reason the your vehicles will be turning. If you track the total amount that each one turns, then you can place them in order, from highest to lowest, by the amount of turning (or change in rotation of the actor) they did. If you needed laps run, you can divide the total amount of rotation by 360.

If you only evaluate the number of laps by the sum of the rotation, then you could turn without driving the track and it is still handled as laps. Maybe you could add checkpoints which every car has to pass in the correct order to finish one lap. (It is possible to create a scoreboard which shows the best 3.)

Yeah, I had thought about that -- like the vehicle spinning out of control racking up the lap count. I did not think that would be an issue here (though, I could be wrong). Using checkpoints is a good idea, however (just more code to deal with).