RWY INCURSION BY A PIC OF A B737 TAXIING TO RWY 18R WHEN HE WAS ONLY CLRED TO RWY 18L AT DFW; TX.

Narrative

WE WERE GIVEN TAXI INSTRUCTIONS TO RWY 18L VIA TXWYS G AND Z. I UNDERSTOOD THE INSTRUCTIONS WERE TO RWY 18R. I DID NOT QUESTION THE INSTRUCTIONS TO RWY 18R DUE TO THE CONSTRUCTION AT THE THRESHOLD OF RWY 18L WHICH HAD A VERT 'X' AND FLASHING LIGHTS. THE FO WAS BUSY WITH ACCULOAD AND COMPLETING CHKLISTS AND DID NOT NOTICE THE XING OF RWY 18L. I VISUALLY CHKED THE FINAL PRIOR TO XING RWY 18L AND HELD SHORT OF RWY 18R. NO TFC ON THE FINAL TO EITHER RWY; ALSO WE WERE THE ONLY ACFT TAXIING AT THE TIME GOING TO RWY 18L/R. IF I HAD SEEN ACFT TAKING OFF ON RWY 18L I WOULD HAVE QUESTIONED THE GND CTLR. I ASSUMED WITH THE THRESHOLD CONSTRUCTION ON RWY 18L THAT THEY WOULD USE THE OTHER RWY WHEN POSSIBLE. IT WAS MY MISUNDERSTANDING OF THE GND CTLR'S INSTRUCTIONS. SUPPLEMENTAL INFO FROM ACN 554152: AS WE WERE TAXIING UP TO RWY 18L AND LOOKING LIKE WE WERE NOT STOPPING AT THE HOLD SHORT FOR RWY 18L; I STATED 'WHERE ARE WE GOING? WE ARE GOING TO PASS THE HOLD SHORT.' THE CAPT STATED WE WERE CLRED TO TAXI TO RWY 18R AND BY THEN WE WERE ON RWY 18L. ON THE OTHER SIDE TWR ASKED WHERE WE WERE GOING; AND I STATED THAT WE MISUNDERSTOOD THE CLRNC AND WE WERE TAXIING TO RWY 18R.