[stevewepay]

I would have thought Market Street is the longest, although it changes its name from Market to Portola to Junipero Serra and then turns into 280.

[sundaeofshock]

The name change is because Market and Portola did not connect until about 1920 or so.

http://sflib1.sfpl.org:82/search?/dStreets+M/dstreets+m/1%2C... http://sflib1.sfpl.org:82/search?/dStreets+M/dstreets+m/1%2C... http://sflib1.sfpl.org:82/search?/dStreets+M/dstreets+m/1%2C... http://sflib1.sfpl.org:82/search?/dStreets+M/dstreets+m/1%2C...

[dnautics]

I would have guessed Geary.