In a town, a set of traffic lights control access from a small road, where a fire station is located, to a main road that has heavy traffic. In times of emergency, many vehicles from the fire station may need to leave the station at the same time. A system is put in place so that when a fire truck on the small road approaches the main road, the traffic lights switch to green (Go) on the small road and to red (Stop) on the main road.