B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
ATC Issue All Types; Conflict Ground Conflict; Less Severe
Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach
Human Factors; Procedure
Had uneventful flight to SFO; and was cleared BIG SUR2 arrival. SFO weather: CAVU night; visibility 20+ miles. Cleared to cross BOLDR at 250/10000 per arrival; then received vectors to the NW; then back to east on a downwind for Runway 28L. Vectored onto a visual final for Runway 28L at about HEMAN; following Aircraft X. We flew the ILS inbound. The preceding Aircraft X appeared to take an inordinate amount to time to clear Runway 28L; exiting I think at taxiway T or K. By now we were within 1.0 nm of threshold. At about 0.75 NM; perhaps even closer; SFO tower cleared another aircraft; Aircraft Y; to 'cross RW 28L'. I believe this aircraft was on E. The aircraft began moving towards; and then onto; RW28L. We were now within 0.5 nm. It was obvious to us that this was not going to work; and we were discussing a go-around. At about 100 feet AGL; Tower directed us to go-around.  The go-around and subsequent approach were uneventful.The SFO tower controller may have lost situational awareness when clearing the other aircraft to cross 28L. At no time were either we; or the other aircraft in any danger. We would have initiated our own go-around within a couple of seconds had the controller not told us to go-around.  Considering that it was a CAVU night; one must wonder what might have happened on a night with reduced visibility if we; and/or SFO Tower; had not been able to see the other aircraft; considering our closeness to the landing threshold. Had we actually landed; this might have been either an accident; or a serious runway incursion.Also; the amount of radio communication occurring was not particularly great; so it was not a matter of any party not being able to get a word in at a critical time.Possible tower controller loss of situational awareness regarding our closeness to runway threshold when clearing another aircraft to cross the runway.
B737 Captain reported he was within one mile of touchdown on SFO Runway 28L when Tower cleared an aircraft to cross the runway. Tower then directed a go-around to resolve the conflict.