How do make laps on game maker?

Have several lines around the track. If a car passes one, set a global variable to +1, only once, and if done in the right order. Once all checkpoints are checked, the finish line may be passed. This makes it so that you cannot drive back and forth across the finish line, and is rather simple to implement. Have it then do it 2 more times. You now have a 3 lap race.