Chicago has a few express buses and is playing with the idea of more. Things like only 1 stop per half mile, a special lane to travel in, raised platforms, and magic that flips traffic signals for them.

http://www.transitchicago.com/ashlandbrt/

They are going for a 16 mph average speed, vs 21 mph that the subway gets. Obviously still a bit slow, but way better than a normal bus (which I think is 5-10 mph)

I know street space is a bit more of a premium in SF over Chicago, but it seems like a pretty good help. Not as good as a subway, but in theory much much cheaper to use, it uses existing streets with just a few rule changes.