San Francisco's cable trams are a great tourist attraction and a priceless example of our industrial and transport heritage. However they aren't part of that city's public transport network in any real sense, and nor is there any idea that they should be.
Well, San Francisco's cable trams are a very real functioning part of the city's public transport.
This from Wikipedia: "The cable cars are principally used by tourists rather than commuters. The system serves an area of the city that is already served by a large number of buses and trolleybuses."
It's not the first time that Wikipedia has been wrong,
and this is such an occasion.
Trolley buses and buses can't get up the steep hills.
They can't use the same street on the hills,
where the cable cars have absolute (repeat absolute) right of way.
On reaching the crest of the hill after one particularly steep climb,
the cable car stops in the middle of the intersection
to pick up or set down passengers.
When the cable car approaches that intersection,
the intersection has to be cleared of all traffic in order that
the cable car can enter and stop there.
Cable cars can't stop on hills, nor give way to vehicular traffic
on hills, simply because they can't stop. Their brakes cannot hold them
on hills, and they rely on the cable for braking while going down hills.
Simply put, cable cars cannot release the grip while going up hills.
If they did, they would run out of control backwards down the hill.