How to change the cable when the tram needs to turn?

The tram doesn't have a throttle, and the driver steps on a variable-speed rheostat.

According to observation, in the sections where trams are separated, the white line signs of "big, medium and small" are painted on the road surface. According to his own model, the driver sends a superposition signal command to the traction electromagnet on the overhead line through the overhead line. At this time, he heard a voice, and the electromagnet worked, turning two overhead lines to another set of lines like a train switch, and then delaying the reset.

This turning zone is obviously isolated from overhead lines.

What is the mechanism of this superposition signal is not clear.

If it is a through train, of course, no signal is needed.

Sometimes the steering fails, but the tram has passed this interval, only to see the conductor get off and pull the rope by hand to shift the pole.