Thanks for the replys. I was hoping not to buy 4 IR sensors, one for each track. I've seen the slot car setup that uses a photocell under the track that triggers when there is less light(car over it at end). I think I've decided on making a contact switch out of two close pieces of copper that connects the circuit when the weight of the car touches them. Freeish and easy. Just have to work to get the connection to be reliable. If anyone has other suggestions please post them!