AN FK10 FLC LANDS THEIR ACFT ON RWY 36 AT DCA; DC. THEY LOST SEPARATION WITH ACFT LNDG RWY 33 AND THEN TURNED OFF RWY 36 ONTO RWY 33 DURING ROLLOUT.

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WE WERE ON VECTORS TO FINAL FOR THE MOUNT VERNON VISUAL TO RWY 36. JUST BEFORE TURNING FINAL TO INTERCEPT THE VISUAL; APCH ADVISED US OF TFC ON VECTORS TO RWY 33. WE RECEIVED THE TURN TO FINAL A LITTLE HIGH AND LATE FOR SEPARATION WITH TFC AHEAD. WE CONFIGURED ACFT FOR LNDG AND SWITCHED TO TWR. TWR CLRED US TO LAND RWY 36; WITH NO MENTION OF ACFT ON APCH TO RWY 33. AFTER TOUCHDOWN AND AS WE WERE BRAKING TO EXIT THE RWY; TWR SAID TURN L ON TXWY S; L ON TXWY J; HOLD SHORT OF RWY 33. FO READ BACK CLRNC; HOWEVER; I HAD ALREADY PLANNED ON TURNING OFF ON RWY 33 FOR TFC BEHIND US; AS TWR HAS ASKED US TO DO MANY TIMES IN THE PAST. I MADE A MISTAKE OF INITIATING A TURN OFF ON RWY 33 WITHOUT CLRNC TO DO SO. AS WE SLOWED TO MAKE THE TURN TWR SAID; ACR DO NOT TURN RWY 33; TFC SHORT FINAL RWY 33. THIS WAS THE FIRST MENTION OF TFC LNDG RWY 33 FROM TWR. WE STOPPED OUR TURN AND CONTINUED TOWARD THE NEXT INTXN. AS WE LOOKED OUT THE R WINDOW ACFT LNDG RWY 33 WAS ALREADY ON THE GO OVERHEAD WITH WHEELS IN THE WELL. I BELIEVE THE ACFT ON RWY 33 WAS TOO CLOSE FOR LNDG EVEN IF WE ROLLED THROUGH THE INTXN. I ALSO THINK THE TWR COULD HAVE USED A DIFFERENT PHRASE TO ALERT US TO THE TFC ON RWY 33. WE WILL BE MORE AWARE OF THIS SIT IN THE FUTURE.