In 1920, the B line, replaced by the busy 38-Geary in 1956, departed from the spot where the Ferry Building stands today and zoomed out to near Ocean Beach in 35 minutes. The fare was a nickel.
Today a similar $2 trip on the 38-Geary takes 54 minutes, while the 38 Limited, which makes fewer stops, takes 43 minutes.
As the article notes, there are reasons for this. Even with a bus not a streetcar, there’s an obvious way to get the speeds back up: cut car traffic back to 1920 levels. (Of course, that’s far more easily written than done.)
(Also, a minor nitpick: the Ferry Building was already over a decade old by 1920.)