If you ever listen carefully to the streets of San Francisco, you’ll hear a low rumble.
No, it’s not the San Andreas Fault acting up again, but the cables running under the tracks of the cable cars.
Made of large metal strands, the cables travel between two huge pulleys, one motorized, at a speed of about nine miles per hour.
One of the two workers on the car pulls a handle to grab onto the cable and start the car with a lurch. Later, when he wants to slow or stop, he releases the grip and the other worker pulls a brake lever that drags along the track.
On any line there are several pulleys along the way, so the cable is released at certain intersections and the car allowed to coast until it reaches the next cable.
The motors that run the pulleys are not incredibly powerful, so the cars are timed so that one coming down a hill helps balance the weight of another going up.