B737-300; CLEARED TO CROSS AN ACTIVE RWY; IS UNABLE TO CLEAR ON OTHER SIDE DUE TO B757; WHICH HAD FAILED TO MAKE A COMPLETE EXIT. CONFLICT WITH LNDG ACFT ENSUES.

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ON LNDG RWY 22R WE WERE DIRECTED TO HOLD SHORT OF RWY 27L FOR LNDG TFC. WE TURNED OFF RWY 22R AT TXWY C AND HELD SHORT. TWR'S INSTRUCTIONS TO THE LNDG ACFT WERE TO TAKE 'C;' IF ABLE; TURN ONTO 'B' AND CONTACT GND CTL ON 121.9. TWR THEN INSTRUCTED US TO 'WITHOUT DELAY; TAXI ACROSS RWY 27L; TURN R ONTO 'B' AND CONTACT GND CTL; TFC ON SHORT FINAL.' AS WE TAXIED ACROSS RWY 27L; BOTH MY COPLT AND I LOOKED AT THE ONCOMING TFC ON SHORT FINAL. FEELING A LITTLE TIGHT; I 'GOOSED' THE THROTTLES TO HURRY ACROSS. AS I LOOKED UP TO GAUGE MY TURN ONTO TXWY B; THERE WAS THE TAIL OF A B757 STILL SITTING ACROSS THE HOLD LINE IN OUR PATH. AS I SLAMMED ON THE BRAKES TO AVOID A COLLISION; I EXCITEDLY; EMPHATICALLY TOLD TWR THAT NEITHER OF US WERE CLR! APPARENTLY; THE B757 HEARD ME AS THEY REALLY CAME ON WITH THE PWR TO TURN ONTO TXWY B AS PREVIOUSLY INSTRUCTED. AS WE CLRED; I WAS SURPRISED TO SEE THE NEXT LNDG ACFT NOT ONLY LAND; BUT TAXI THROUGH THE 'C' INTXN. I FULLY EXPECTED IT WOULD HAVE TO BE SENT AROUND.