This is a solution to the Race Track challenge. The secret here is to use the coloured corners of the car to detect when the car is about to steer off the track. You can adjust the angle of the car depending on which colour is touching the background.
How fast can you make your racing car drive without spinning off the track? This project was inspired by this BBC Bitesize Computing video: http://www.bbc.co.uk/guides/z23q7ty#zqjyvcw