RWY INCURSION BY MD88 UPON TAXI OUT FROM GATE. A PROPOSED RWY CHANGE WAS IN PROGRESS.

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ACFT HAD PUSHED OFF GATE AND REQUESTED TAXI CLRNC. GND CTL CLRED TAXI TO RWY 09 WITH RESTR TO HOLD SHORT OF RWY 04. DUE TO CLOSE PROX OF RWY 27; FO ASKED CAPT IF RWY 27 WERE AVAILABLE WOULD HE PREFER TO USE IT. CAPT REPLIED YES; AND FO MADE REQUEST TO GND CTL. AFTER OBSERVING SEVERAL SMALL ACFT IN THE PATTERN; CAPT TOLD FO TO REQUEST TO JUST STAY WITH RWY 09 AND STARTED ACFT FORWARD. FO DID SO BY TELLING GND CTL WE WOULD PREFER TO USE RWY 09 AS DIRECTED. GND CTL 'ROGERED' OUR REQUEST. CAPT MADE A TURN ONTO TXWY A AS HE HAD BEEN CLRED TO DO AND MENTIONED HIS REASONS FOR CHANGING HIS MIND TO FO. CAPT WAS CONCURRENTLY LOOKING OUTSIDE FOR TFC AS HE WAS TALKING; LOOKING TO ENSURE TXWY D WAS CLR; AND AT THAT TIME FELT THE BRAKE PEDDLES MOVING TO STOP THE ACFT. AT THE SAME TIME GND CTL XMITTED 'STOP' TO OUR ACFT. THE SHIP WAS STOPPED QUICKLY BUT NOT SO MUCH SO THAT THE FLT ATTENDANTS WERE NOT THROWN ABOUT AS THEY WERE STANDING AND GIVING THEIR DEMO. THE ACFT STOPPED BEYOND THE RWY 04 HOLD LINE BUT PRIOR TO ACTUALLY ENTERING THE RWY SURFACE. THE PRIMARY REASON I WOULD ATTRIBUTE FOR THIS EVENT OCCURRING IS THE VERY SHORT DISTANCE SEPARATING THE RAMP AREA -- TXWY D AND RWY 04. TXWY D WAS PASSED WHILE CAPT WAS TALKING AND LOOKING OUTSIDE FOR AIRBORNE ACFT. RWY 04 IS A 75 FT WIDE RWY AND HAS THE 'LOOK' OF A TXWY AND IS VERY CLOSE TO THE RAMP AREA. IT IS EXTREMELY EASY TO MISTAKE IT FOR A TXWY WHICH IS EXACTLY WHAT HAPPENED IN THIS INSTANCE. CORRECTIVE MEASURES POSSIBLE: BETTER SITUATIONAL AWARENESS BY THE CREW. BETTER RWY AWARENESS. ELIMINATION OF SIMULTANEOUS USE OF CONFLICTING RWYS. SUPPLEMENTAL INFO FROM ACN 353571: WE STOPPED THE ACFT NOSE BEYOND THE HOLD SHORT LINE BUT APPROX 20 FT SHORT OF RWY 4. ACFT ON SHORT FINAL WAS DIRECTED TO GAR AS WE HELD SHORT OF THE RWY.