Actually, I'd say it really comes down to rails and tires. Streetcars can be given the same rights-of-way as buses and would perform similarly, except: the streetcar is a smoother ride. I can grab breakfast and eat it on a streetcar knowing there's only one direction of motion to worry about. On a bus, however, you can never tell which way you'll be jerked around. It really is much less pleasant, even if it's faster without the right of way. (Due to left turning cars)
Can someone who's taken the new MTA Select Bus Service busses comment on whether they are smoother than regular busses? I took an MTA bus today for the first time in a long while and it was uncomfortably bumpy.
I haven't taken them very often, but I have had a couple really great experiences with the M15 1st/2nd Ave SBS. Due to cascading traffic lights, efficient boarding, and wide spacing between stops, it's almost as nice as taking the subway.
