Originally Posted by
sfogate
There are 3 ways to get from T-1 to T-3:
1. Shuttle van service which operates inside the security zone. From the T-3 terminal you can pick it up at Gate 71-A (located just after the check point and Yankee Restaurant) or at Gate 87-A. The only elevator access is at Gate 87-A. From T-1 to T-3: look for signs in the gate area. Van service stops at 11pm.
2. AirTrain is the tram the runs around the airport and rental car terminal. This is pre-security and operates 24 hours.
3. You can walk.
You forgot #4 - Take the SFO Parking Shuttle (only works from T1 to T3 unless you want to see the SFO long term parking garage on the way from T3 to T1)
If you're flying at peak hours and don't have CLEAR or pre-check access (once it comes to SFO) then the shuttle van is most likely your best bet to avoid hassling with security again)