Definitely a cable car - that’s the third slot in the middle between the rails. It has a moving cable in it. When the operator wants to go, he pushes his big lever which clamps on to the cable and the car goes forward. When he wants to stop or slow down, he releases the clamp. Still done the same way today, and if I’m not mistaken, the only active cable car system in teh world.
The thing I didn’t get was the kid who was riding his bike in front of the car - he went right over the cable slot but didn’t fall in.