RWY INCURSION OCCURS WHEN THE PIC OF A DO328 CROSSES THE HOLD LINE IN ANTICIPATION OF A TKOF CLRNC AFTER FO HAD RESPONDED IN THE AFFIRMATIVE TO THE TWR'S QUESTION OF BEING READY FOR TKOF AT DCA; DC.

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WHILE TAXIING FOR TKOF ON RWY 1 AT DCA; I SWITCHED TO TWR FREQ AS WE NEARED THE BEGINNING OF THE RWY. JUST AFTER SWITCHING; TWR CALLED AND ASKED IF WE 'WERE READY.' I IMMEDIATELY REPLIED THAT WE WERE 'READY;' BUT GOT NO RESPONSE. IN THE MEANTIME; THE CAPT -- APPARENTLY UNDER THE ASSUMPTION THAT A TKOF OR POS AND HOLD CLRNC WOULD BE ISSUED AFTER MY RESPONSE OF BEING 'READY' -- FAILED TO SLOW THE ACFT DOWN; AND BEFORE I COULD SAY ANYTHING; WE HAD CROSSED THE HOLD SHORT LINE ONTO THE RWY. THANKFULLY; THERE WERE NO ACFT ON FINAL FOR ANY RWY WHEN THIS OCCURRED. I ONCE AGAIN TOLD TWR THAT WE WERE 'READY' AND TWR CLRED US FOR TKOF AFTER SAYING HE WAS DISTR AND THUS DID NOT ISSUE THE CLRNC EARLIER. IN MY OPINION; THIS INCIDENT WAS CAUSED BY THE CAPT'S ASSUMPTION THAT A TKOF CLRNC WOULD BE ISSUED IMMEDIATELY; SINCE THERE WERE NO ACFT ON FINAL. HAD THERE BEEN AN ACFT ON FINAL; I WOULD HAVE USED MY BRAKES TO PREVENT AN INCURSION. IN THE FUTURE; THIS TYPE OF INCIDENT COULD BE PREVENTED BY HAVING BOTH CREW MEMBERS VERIFY ANY TKOF OR POS AND HOLD CLRNC BEFORE THE ACFT IS ALLOWED TO CROSS THE HOLD SHORT LINE.