I ride them every time I'm in San Fransisco, does that count?
Sort of. You will note that street cars are different from cable cars. Jack's picture shows a street car, which is powered be electricity via a top wire. It runs on what are basically train tracks.
San Francisco does have those running up and down Market st (and looping around the Embarcadero to Fisherman's Wharf... and all the way to the Castro district in the other direction):
If you look at the closely on the street, you might recognize some of them from your childhood. The city has bought decommissioned streetcars from places like Boston, Brooklyn, Louisville, Los Angelos etc. They have been restored and are now functional (actually used by residents, as well as some tourists) pieces of history.
Our modern subway system also employs "street-cars" that in the western part of the city immerge from the subway and operate on street level. The technology behind these is virtually identical to the one's in Jack's picture. Electric wires above, train type track below.
BUT What you guys are probably thinking of in San Francisco are Cable Cars. These are powered by a moving cable underground, and no electricity is involved (no wires above the car). These were once used from the Bay almost all the way out to the ocean all across town. While the city is not very big (area-wise), the hills did present transit problems in the old days, so these cable cars were the earliest form of public transportation in The City. The 3 lines still operating are primarily used by tourists, although some residents do use them (the routes and speed at which they move are not conducive to using them for everyday transportation).
Sorry, you stumbled upon one of my obsessions :com: