Another thing about cable cars dropping and re-grabbing the cable (which, BTW, is called “rope” in the cable car biz, per that pamphlet):
When the claw is grabbing the rope, it also pulls up on it a bit. When it lets go, the rope drops down a bit, just outside of reach of the claw.
To grab the rope again, the car must dip down a bit. There are very specific places along each route where the driver is supposed to do this. At these spots, there is a dip built into the roadway. The operator has to grab the rope just as the car passes through that dip (which, I think, is in a place where the car would be stopping anyway, so the driver doesn’t have to grab it on the fly with split-second precision).
There is one such spot clearly visible near the Cable Barn. IIRC, it’s just a block or maybe just a half-block uphill from the barn. After I read about it in that pamphlet, the next time I visited San Francisco I made it a point to go see it myself.
There is a sign posted at the spot, with instruction “Take rope”. I’m sure the driver already knows that, though.
Just found this blog by rail fan “Jersey Mike” with extensive excellent photos of San Francisco cable cars, including pics and some comments about the crossing at California and Powell. ETA: He links to more pics from a previous expedition here.
On reading further from the link in post #52, it appears they do it both ways:
So, even when connected to the cable on a downgrade the brakes are still applied and the cable is pulling the car downhill against the brakes. To stop, the cable is released and the brakes bring the car to a halt. The downside to this method is that the car is still travelling at 9.5 mph which may be a bit too fast for a quick stop. The advantage to “walking” the car downgrade (coasting with the cable released) is that the car can be held to a slower pace, and can stop in a shorter distance. Also, while it wasn’t mentioned in the text, I wonder if riding the cable downgrade would “stretch” the cable and cause the car to “push” some cable slack ahead which might cause alignment problems in the cable possibly causing it to jump a guide on curves or even on the main drive sheave.
So, what happens if a cable car lets go of the rope anywhere other than one of the “Take Rope” dips? Does everyone need to get out and push to reach the nearest dip?
No…if there is no declivity in the street, there may be a “gypsy”–a lever in the street, flush with the street surface, that lifts pulleys that lift the cable at that spot. The gripman also has a hooked stick he can stick into the slot, just behind the grip jaws, to lift the cable.
If a cable car has to drop the cable on a hill, they will back down to the bottom of the hill to re-acquire the cable. You’ll hear the conductor ringing his bell (“dink-dink”) as the car backs down…if there are any cars in the way, they’ll have to back down too. The locals, if they’re feeling helpful, will sometimes assist in directing traffic…
I can’t see the Hyde Street car backing down Russian Hill–on the north side from loss of the cable, all the way down from Francisco to North Point! That’s pretty far! :eek:
That works ok for a gondala/barge system, where everything is going around and no one minds the waits for a stop. Or for the barge system, its only going to do two at a time, one up one down but there’s a queue of barges waiting. The points are that the slopes are constant, the vehicles are all the same loading, and there so the variability of the load is rather well controlled… there’s no large random changes midjourney.
Its obviously impractical to have all cable cars come to a stop when one is at its stop… the other cars would be blocking the roads, and if one HAS to reverse, due to a traffic jam, they’d all have to reverse. So thats why they must be able to detach.
Now the detaching and attaching would make speed surges…
There’d have to be a sophisticated braking system, and it would wanna be ready, so it’d have to be predicatively operated …“braking system on now, two seconds early !”. And if the cable speed controller was to fail, then the cable cars going down hill may well surge forward at great acceleration… before the driver could get to his own brakes… Something they wouldn’t be used to, and it would then cause the situation that some drivers just let the other drivers do the braking… which could sometimes fail if all drivers assume someone else will do it… Rather dangerous to other traffic… Well anyway braking is horribly complicated, so each car is responsible for that. They just don’t have any motive power inbuilt, so they climb by grabbing hold of the rope.
The reason its safe enough to have them climb by rope is that there is time for the driver to get to the brakes should the car start to roll backward down the slope. And they all know that if that happens, thats what they have to do, as it only happens in some rare failure. (not merely because there happens to be a few more cars down uphill than downhill… )
I’m specifically thinking about Jackson St. When I say they back down the hill, I really mean they back down to the last “Take Rope” spot. On Jackson St. that works out to be the last intersection.
Normally, the operator will make sure the street is clear (i.e. no double parked vehicles, etc…) before taking the rope. If someone’s double parked (e.g. an Uber pickup) or trying to park inappropriately you’ll hear the crewing ringing the bell and shouting at them to get out of the way.
Oh, sure, the balance won’t be exact. That’s why you need the motors, after all. But the balance would be a lot closer with the downhill cars gripping than with them being loose.
Well, the downhill cars are (ideally) ALL gripping the cable. A six-ton car speeding down an 18% grade—well, that’s not a wise idea, to put it mildly. The track- and wheel - brakes would be useless in such a situation.