Narrative:

CAT III (1000 ft RVR) approachs were in progress at sfo, runway 28R. On short final tower had asked us to exit on taxiway east (left turn). We exited on taxiway east and with clearance taxied across runway 28L on taxiway east. Once we were clear of runway 28L we stopped and got taxi instructions from ground control. They were, 'taxi B, H, to the gate.' the visibility at the intersection of txwys east and B where we had stopped was very low. It was impossible to see the island separating taxiway a from taxiway B to the southeast, or any other taxiway sign in that direction except txwys J and B. Under the existing conditions it was impossible to tell if a left turn would be on to taxiway J or B. Taxiway J would be a bad idea as it leads to runway 28L. So, with the airport map in front of us it appeared that taxiway B was slightly ahead. After moving approximately 150 ft ahead the international terminal started to come into view. We were entering taxiway a. A hard left turn would put us on taxiway B or would it be taxiway J? In any event I felt uncomfortable turning back left, without guidance and in low visibility conditions, toward runway 28L. So I reported to ground that we were entering taxiway a. They confirmed our position and cleared us taxiway a, taxiway H to the gate. In low visibility conditions, this intersection is very uncomfortable as presently marked, and I'm very familiar with this airport. As I said the only sign we saw was the taxiway J/B sign to our left. Numerous yellow taxi lines were under us where we had stopped after exiting runway 28L, but none was marked. We saw no other taxiway signs heading southeast until entering taxiway 'a' when I saw an upside down taxiway B painted on taxiway a indicating that taxiway B was straight ahead for someone taxiing the opposite direction on taxiway a. Some markings on the yellow taxi lines as they cross/diverge at the intersection of txwys east and B would have been very helpful. This intersection is just too big to see taxiway signs off in the distance under low visibility conditions. Callback conversation with reporter revealed the following information: tower supervisor stated the area in question could cause some confusion during low visibility operations. The signage and markings are standard and not much else can be done. Sfo will soon implement a new surface movement guidance and control system.

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Original NASA ASRS Text

Title: ACR NON ADHERENCE TO ATC CLRNC UNAUTH TXWY EXCURSION DURING LOW VISIBILITY.

Narrative: CAT III (1000 FT RVR) APCHS WERE IN PROGRESS AT SFO, RWY 28R. ON SHORT FINAL TWR HAD ASKED US TO EXIT ON TXWY E (L TURN). WE EXITED ON TXWY E AND WITH CLRNC TAXIED ACROSS RWY 28L ON TXWY E. ONCE WE WERE CLR OF RWY 28L WE STOPPED AND GOT TAXI INSTRUCTIONS FROM GND CTL. THEY WERE, 'TAXI B, H, TO THE GATE.' THE VISIBILITY AT THE INTXN OF TXWYS E AND B WHERE WE HAD STOPPED WAS VERY LOW. IT WAS IMPOSSIBLE TO SEE THE ISLAND SEPARATING TXWY A FROM TXWY B TO THE SE, OR ANY OTHER TXWY SIGN IN THAT DIRECTION EXCEPT TXWYS J AND B. UNDER THE EXISTING CONDITIONS IT WAS IMPOSSIBLE TO TELL IF A L TURN WOULD BE ON TO TXWY J OR B. TXWY J WOULD BE A BAD IDEA AS IT LEADS TO RWY 28L. SO, WITH THE ARPT MAP IN FRONT OF US IT APPEARED THAT TXWY B WAS SLIGHTLY AHEAD. AFTER MOVING APPROX 150 FT AHEAD THE INTL TERMINAL STARTED TO COME INTO VIEW. WE WERE ENTERING TXWY A. A HARD L TURN WOULD PUT US ON TXWY B OR WOULD IT BE TXWY J? IN ANY EVENT I FELT UNCOMFORTABLE TURNING BACK L, WITHOUT GUIDANCE AND IN LOW VISIBILITY CONDITIONS, TOWARD RWY 28L. SO I RPTED TO GND THAT WE WERE ENTERING TXWY A. THEY CONFIRMED OUR POS AND CLRED US TXWY A, TXWY H TO THE GATE. IN LOW VISIBILITY CONDITIONS, THIS INTXN IS VERY UNCOMFORTABLE AS PRESENTLY MARKED, AND I'M VERY FAMILIAR WITH THIS ARPT. AS I SAID THE ONLY SIGN WE SAW WAS THE TXWY J/B SIGN TO OUR L. NUMEROUS YELLOW TAXI LINES WERE UNDER US WHERE WE HAD STOPPED AFTER EXITING RWY 28L, BUT NONE WAS MARKED. WE SAW NO OTHER TXWY SIGNS HEADING SE UNTIL ENTERING TXWY 'A' WHEN I SAW AN UPSIDE DOWN TXWY B PAINTED ON TXWY A INDICATING THAT TXWY B WAS STRAIGHT AHEAD FOR SOMEONE TAXIING THE OPPOSITE DIRECTION ON TXWY A. SOME MARKINGS ON THE YELLOW TAXI LINES AS THEY CROSS/DIVERGE AT THE INTXN OF TXWYS E AND B WOULD HAVE BEEN VERY HELPFUL. THIS INTXN IS JUST TOO BIG TO SEE TXWY SIGNS OFF IN THE DISTANCE UNDER LOW VISIBILITY CONDITIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: TWR SUPVR STATED THE AREA IN QUESTION COULD CAUSE SOME CONFUSION DURING LOW VISIBILITY OPS. THE SIGNAGE AND MARKINGS ARE STANDARD AND NOT MUCH ELSE CAN BE DONE. SFO WILL SOON IMPLEMENT A NEW SURFACE MOVEMENT GUIDANCE AND CTL SYS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.