AFTER LNDG RWY 28R AT BIL; FLT CREW EXITED AT TXWY D AND WAS CLRED 'TO PARK' VIA THE LCL CTLR. TOOK RTE UNINTENDED BY CTLR AND CROSSED RWY 7-25 ENRTE TO PARKING.

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AFTER LNDG ON RWY 28R; THE TWR CTLR INSTRUCTED US TO 'TURN L ON TXWY D; TAXI TO PARK.' I READ BACK THE FOLLOWING 'L ON DELTA; TAXI TO PARK WITH YOU.' THE CAPT CALLED FOR THE AFTER LNDG CHKLIST AND I STARTED ON THAT. THE CAPT TURNED R ONTO TXWY A; CROSSED RWY 7 AND TURNED L ONTO TXWY G. THE TWR CTLR CONTACTED US AFTER WE TURNED ONTO TXWY G AND SAID 'ACFT X; IN THE FUTURE; USE TXWY J SO YOU DON'T HAVE TO CROSS RWY 7.' I REPLIED 'ROGER; WE'LL USE TXWY J IN THE FUTURE.' THE CAPT QUERIED THE TWR CTLR ABOUT THIS STATEMENT; AND THE CTLR SAID '...IT IS EXPECTED FOR YOU TO USE TXWY J.' RWY 7 WAS NOT ACTIVE OR IN USE AT THE TIME OF THE INCIDENT. MY UNDERSTANDING OF THE AIM IS THAT A 'TAXI TO PARK' OR 'TAXI TO RAMP' CLRNC CLRS YOU TO CROSS ALL RWYS AND TAXI INTXNS ON THE WAY TO THE RAMP OR PARKING AREA. BY THE TIME I COMPLETED THE AFTER LNDG CHKLIST; WE WERE TURNING L OFF OF TXWY A ONTO TXWY G. I SHOULD HAVE BEEN MORE ALERT AND QUERIED THE CAPT WHY HE TURNED ONTO TXWY A INSTEAD OF XING TXWY A ON TXWY D; THEN TURNING R ON TXWY J. USING TXWY J IS SHORTER THAN USING TXWY A AND I CAN UNDERSTAND WHY THE CTLR ASSUMED THE CAPT WOULD USE IT (TXWY J). OTHER CTLRS EITHER ADD 'VIA TXWY J' TO THEIR INSTRUCTIONS; OR DON'T CARE WHICH WAY YOU TAKE. I COULD HAVE QUERIED THE CTLR; BUT THERE ARE SO MANY INSTANCES WHERE THE CTLRS GIVE US THIS SAME CLRNC 'TURN L ON TXWY D' (OR WHATEVER TXWY) 'TAXI TO PARK;' AND NOTHING IS EVER SAID. THE CAPT HAD COMPLAINED ABOUT HAVING A HEADACHE ON THE OUTBOUND LEG. THIS MAY HAVE AFFECTED HIS JUDGEMENT. I DON'T SEE WHAT WE DID AS WRONG. WE WERE FOLLOWING THE CLRNC WE WERE GIVEN. THE PROB IS THAT THE CTLR EXPECTED US TO DO ONE THING; AND WE DID ANOTHER; WHICH WAS STILL IN ACCORDANCE WITH HIS INSTRUCTIONS. WE AS PLTS SHOULD QUERY ATC IF THERE IS MORE THAN 1 WAY OF COMPLYING WITH A TAXI CLRNC. ALSO; ATC NEEDS TO SPECIFY THEIR PREFERRED RTE IF THERE IS MORE THAN 1 WAY TO COMPLY. IN ADDITION; THE CTLR HAD LOTS OF TIME TO TELL US TO DO A 360 DEG TURN ON TXWY A AND USE TXWY J. WE WENT ON ANOTHER FLT LATER THAT DAY; AND LANDED ON RWY 28R AND EXITED AT TXWY D. THIS TIME THE CTLR CLRED US TO 'TAXI TO PARK VIA TXWY J.' PROB SOLVED.