A B737 FLC ON EXPRESSWAY CHARTED VISUAL APCH TO LGA RWY 31 EXTENDED THEIR FLT PATH TO ACCOMMODATE ADDITIONAL TFC SEQUENCED AHEAD OF THEM. A GAR WAS INITIATED ON FINAL APCH DUE TO THE CLOSE PROX OF THE ACFT IN FRONT AND A TCASII RA. BOTH CREW MEMBERS WERE CRITICAL OF ATC HANDLING.

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OUR ACFT X WAS ON THE EXPRESSWAY VISUAL (CHARTED) TO RWY 31 AT LGA. AS WE APCHED THE TURN-ON TO FINAL POINT AT THE SHEA STADIUM AREA; TWR ISSUED THE INTERVAL TFC WE WERE TO FOLLOW. THIS TFC; INSTEAD OF BEING ON THE GND TRACK EXPECTED; WAS 3 MI OR SO EXTENDED ON THE 130 DEG RADIAL OR EXTENDED CTRLINE OF RWY 31. WE; THEREFORE; HAD TO TURN R; THEN 180 DEGS BACK AROUND TO PROVIDE SEPARATION. AS WE CAME AROUND AND BEGAN AN EXTENDED FINAL AND DSCNT TO THE RWY; TWR ISSUED A TFC CALL AT OUR 10 O'CLOCK UNKNOWN ACFT Y AT 1700 FT; APPROX 2 1/2 MI; NOT TALKING TO TWR. WE CONTINUED TOWARD THE RWY AND WATCHED THE TFC COMING DIRECTLY TOWARD US APPARENTLY ON THE EXPRESSWAY VISUAL FOR RWY 31. TWR TRIED TO NOTIFY ACFT Y OF HIS NEED TO SEQUENCE BEHIND US BUT WAS BLOCKED BY THE OTHER ACFT FINALLY XMITTING FOR CLRNC TO LAND. OUR SEPARATION WAS GETTING UNSATISFACTORY AND IT BECAME OBVIOUS THAT THE OTHER ACFT (ACR Y) WAS GOING FOR THE RWY AT THE SAME TIME AND WE WOULD COLLIDE. SO WE EXECUTED A MISSED APCH AND FINALLY WERE ABLE TO GET AN ALT AND HDG FROM TWR FOR ANOTHER APCH. THE CONTRIBUTING FACTORS WERE (IN MY OPINION): 1) CHARTED VISUAL USED WHEN TFC DENSITY WAS TOO GREAT. EACH ACFT SEQUENCED SHOULD BE ABLE TO FOLLOW INTERVAL AHEAD ON THE SAME TRACK; OTHERWISE PLT WORKLOAD BECOMES TOO HIGH LOOKING FOR VISUAL CUES; TFC; RWY; ETC. 2) OTHER ACFT NOT IMMEDIATELY CONTACTING TWR FOR SEQUENCING. WHEN IT DID COMMUNICATE; IT WAS SLOW AND FREQ CONGESTING NOT ALLOWING FOR ADVISORIES. 3) POSSIBLE POOR COORD BTWN NY APCH AND LGA TWR; ALLOWING DENSITY IN THE ATA TO BECOME UNMANAGEABLE. SUPPLEMENTAL INFO FROM ACN 361991: WHILE WE WERE ON 3 MI FINAL; ACFT Y DID NOT EXPECT US TO BE ON AN EXTENDED FINAL WHILE FOLLOWING THEIR DEPICTED GND TRACK. THEY WERE NOT IN CONSTANT CONTACT WITH TWR AND ASSUMED THEY WERE #1 AFTER BEING CLRED THE EXPRESSWAY VISUAL RWY 31 AND DID NOT LOOK FOR US. IT IS EASY TO BECOME PREOCCUPIED WITH TRYING TO IDENT THE LANDMARKS AND RWY AMONG ALL OF THE GND LIGHTS AND NOT CLR FOR TFC NOT FLYING THE GND TRACK. I DO NOT THINK TWR SHOULD EXTEND OUR FINAL WHILE STILL CALLING IT THE EXPRESSWAY VISUAL RWY 31. TWR AND ACFT Y WERE NOT IN CONSTANT CONTACT. EITHER ACFT Y DID NOT CHK IN OR TWR MISSED THE HDOF FROM APCH CTL. TWR SHOULD CANCEL THE EXPRESSWAY VISUAL RWY 31 ONCE PLANES DEVIATE FROM THE DEPICTED GND TRACK. THEY SHOULD ALSO TELL THEM THAT THE TFC IS ON EXTENDED FINAL AND NO LONGER FLYING THE EXPRESSWAY VISUAL.