[gdne]

Because most of the transportation operates on public streets (busses and muni). This forces them to deal with traffic and pedestrian crowds, which make them no better than driving. If SF had a real subway system, things would probably be different.

[al_gore]

The Green Line in Boston runs down a protected center path in the road for a significant portion. Is there a reason that SF can't carve out those lanes for exclusive Muni use?

[nerfhammer]

There's actually one case where they're trying to do this:

http://sf.streetsblog.org/2012/06/27/options-for-geary-brt-c...

[bowlofpetunias]

Plenty of cities don't have a subway but do have decent public transport that rarely gets stuck in traffic. Separate bus and rail lanes help.

SF, like most US cities, reserves ridiculously wide roads for car traffic.