MULTIPLE FACTORS LEAD TO AN ACR CAPT MAKING SEVERAL ASSUMPTIONS ABOUT THE TAXI ROUTING THAT WERE NOT CORRECT. THE FO RAISES THE QUESTION THAT CAUSES THE CAPT TO STOP THE ACFT SLIGHTLY OVER A HOLD SHORT LINE OF THE ARR RWY.

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WE WERE CLRED TO TAXI TO RWY 4. AFTER MAKING A R TURN COMING OUT OF PARKING; THE CAPT TAXIING THE ACFT; NOTICED AN ACFT JUST CLRING THE RWY AND STOPPING TO OUR R AND AN ACR Z JET HDG N ON TXWY K. NORMALLY BEING TOLD TO TAXI AROUND OR BEHIND THE CLRING ACFT; AND ASSUMING THAT WOULD BE OUR CLRNC; THE CAPT (MYSELF) TAXIED STRAIGHT ON TXWY S INSTEAD OF MAKING A R TURN ON TXWY N AND CROSSED THE HOLD LINE AT THE FAR END OF RWY 33. THE FO; HAVING BEEN OFF FREQ MOMENTARILY; ASKED THE CAPT WHICH RWY WE WERE USING FOR TKOF. UPON REALIZING THAT WE WERE HEADED FOR AN ACTIVE RWY; WE IMMEDIATELY STOPPED ON THE TXWY; SHORT OF RWY 33. THERE WAS A BEECH 99 (NOT SURE WHAT TYPE; TOO FAR AWAY) CLRING DOWNFIELD AT EITHER TXWY M OR TXWY N (AGAIN NOT SURE WHAT TXWY BECAUSE OF DISTANCE). AT NO TIME WAS ANY ACFT IN JEOPARDY OR IN CLOSE VICINITY OF ANOTHER. I THINK THAT IT BEING A HABIT OF EXPECTING WHAT WE NORMALLY HEAR; DOING WHAT WE NORMALLY EXPECT AND BEING COMFORTABLE IN AN OPERATING [ENVIRONMENT] SUCH AS DCA (EXCELLENT CTLRS); CAN LEAD TO AN EVENT SUCH AS THIS.