Narrative:

Pushed back from gate xx and was cleared to taxi to runway 28. Captain taxied west around fire station and mistook taxiway east for taxiway P/P1. We realized our mistake but it was too late to stop and entered runway 28. We had cleared (looked for traffic) as we crossed and the only traffic was taxiing towards the approach end of runway 28. The traffic was not on the runway and was no conflict. The runway and taxiway markings at this location taxi east/runway 28, taxiway P/P1/runway 4 are somewhat confusing and have been a problem in the past for others (we were told).

Google
 

Original NASA ASRS Text

Title: B737-500 ACFT. FLC MISTOOK TXWY AND ENTERED ONTO A RWY. THEY THEN CROSSED THE RWY WITH NO CONFLICTS. TXWY MARKINGS AT THAT LOCATION ARE CONFUSING.

Narrative: PUSHED BACK FROM GATE XX AND WAS CLRED TO TAXI TO RWY 28. CAPT TAXIED W AROUND FIRE STATION AND MISTOOK TXWY E FOR TXWY P/P1. WE REALIZED OUR MISTAKE BUT IT WAS TOO LATE TO STOP AND ENTERED RWY 28. WE HAD CLRED (LOOKED FOR TFC) AS WE CROSSED AND THE ONLY TFC WAS TAXIING TOWARDS THE APCH END OF RWY 28. THE TFC WAS NOT ON THE RWY AND WAS NO CONFLICT. THE RWY AND TXWY MARKINGS AT THIS LOCATION TAXI E/RWY 28, TXWY P/P1/RWY 4 ARE SOMEWHAT CONFUSING AND HAVE BEEN A PROB IN THE PAST FOR OTHERS (WE WERE TOLD).

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.