Speedy electric commuter trains take people from small towns to work in big cities. In a tunnel, a red signal light tells the engineer in the cab to stop. She waits until the other train is out of sight. When it is far away, the light will turn green. Then the engineer knows it is safe to go on.
Special trains do special jobs.
Busy little mining trains bring ore out of the mine. Side-tipping cars dump loads of ore onto waiting barges. At the steel mill, hot liquid metal is poured into special tank cars with many wheels. The top of another kind of car tips open to take in a hot metal bar called an ingot. When a diesel locomotive needs repairs, it goes to a diesel repair shed.