Stop and Go on the Railroad. Model signals fulfill important control and safety functions just like those of the prototype. Märklin signals control traffic, because they not only show prototypical signal aspects, they also directly influence the movement of trains. When set for "stop" they turn off current in their area to the center rail and to the catenary - the train remains stopped. When set for "slow" or "full speed" they turn the current on - the train travels through the area or starts up again. If you want to be even more realistic, you can set up distant signals at the proper intervals; these are connected in tandem with their home signals and show the same signal aspects. Color light and semaphore/target signals are controlled with the 7272/72720 control box and in the Digital system with the accessory decoders. In conjunction with circuit tracks or reed switches, signals can also be controlled by trains in operation, thereby automating many operating procedures.