TKOF CLRNC GIVEN AND RESCINDED AFTER START OF THE TKOF ROLL DUE TO APCHING TFC ON XING RWY AT LGA; NY. TKOF WAS CONTINUED.

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WE WERE CLRED FOR TKOF ON RWY 13 LGA; WITH LNDG TFC ON APCH TO RWY 4. AFTER TOGA THRUST WAS SET AND OUR ACFT WAS ROLLING; TWR GAVE US INSTRUCTIONS TO HOLD OUR POS. WITH LITTLE TIME TO REACT; AND OUR ACFT ACCELERATING RAPIDLY TOWARD THE RWY 4 INTXN; THE CAPT DECIDED TO CONTINUE THE TKOF ROLL. FO REPLIED 'UNABLE' TO THE 'HOLD POS' CLRNC. WE PASSED THROUGH THE RWY INTXN WELL BEFORE THE LNDG TFC TOUCHED DOWN. AFTER TKOF; WE DISCUSSED WHAT HAD HAPPENED. WE BOTH AGREED THAT IF WE HAD TRIED TO STOP ON THE RWY (ABORT); WE MIGHT HAVE ENDED UP RIGHT IN THE INTXN; WHICH WOULD HAVE CAUSED A BIG PROB. CONTINUING THE TKOF WAS THE RIGHT THING TO DO. ATC SEEMS TO BE TRYING HARDER AND HARDER TO GET MORE ACFT IN AND OUT OF THESE BUSY ARPTS; AND SEPARATION DISTANCES HAVE DECREASED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR INDICATED THAT THE OTHER ACFT WAS A TURBOPROP COMMUTER TYPE ACFT THAT WAS ESTIMATED TO BE 3000 FT OUT ON FINAL APCH TO RWY 22. THE SEPARATION OF THE ACFT WOULD HAVE BEEN AN ESTIMATED 5000 FT AS THE RPTR CROSSED THE INTXN. THE RPTR'S COMMENT WAS THAT THERE WAS 'NO CONFLICT' AND HIS CONCERN WAS THAT TO REJECT THE TKOF AT THE POINT CLRNC WAS CANCELED WOULD HAVE CREATED ONE. THE TERMINOLOGY USED TO CANCEL THE CLRNC WAS SOMETHING TO THE EFFECT OF 'NEW PLAN ACR XXX; HOLD YOUR POS.' BY THIS TIME; THE TKOF HAD ALREADY BEGUN; THE ACFT WAS LIGHT AND ACCELERATION WAS RAPID; WHICH ALL CONTRIBUTED TO THE DECISION THAT WAS MADE TO CONTINUE.