DC9 CREW INBOUND TO LGA IS GIVEN THE EXPRESSWAY VISUAL RWY 31 APCH PROC. THE TWR APPARENTLY FELT THE SPACING WITH THE TFC AHEAD WAS A LITTLE TIGHT AND ISSUED 2 VECTOR HDGS TO INCREASE THE SEPARATION SLIGHTLY.

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WE ARRIVED LGA ON THE MILTON 1 ARR. ATIS INFO; CURRENT AT THE TIME; TOLD US TO EXPECT THE LDA A RWY 22 AT LGA. SHORTLY AFTER BEING HANDED OFF TO FINAL APCH CTLR; WE HEARD THE CTLR ISSUING CLRNCS FOR THE EXPRESSWAY VISUAL TO RWY 31 AT LGA -- EVEN THOUGH THIS APCH WAS NOT ON THE CURRENT ATIS. WE QUICKLY REVIEWED THE EXPRESSWAY VISUAL APCH AND BEFORE WE HAD A CHANCE TO CHK ON TO THE FREQ; WE WERE CLRED FOR THE EXPRESSWAY VISUAL TO RWY 31. WE PROCEEDED TO THE DIALS INTXN VIA THE PETHS NDB. AFTER PETHS WE PROCEEDED ON A 085 DEG HDG PER THE EXPRESSWAY VISUAL TO RWY 31. LGA TWR THEN ISSUED TFC FOR US IN OUR 10 O'CLOCK POS ON FINAL FOR RWY 31. AS WE WERE LOOKING FOR THE TFC; LGA TWR GAVE US A 130 DEG HDG. AFTER WE COMPLETED THE TURN TO A 130 DEG HDG; WE RPTED THAT WE HAD THE TFC IN SIGHT. LGA TWR THEN TOLD US TO 'FOLLOW THE TFC; CLRED FOR THE VISUAL RWY 31.' WE CONTINUED ON THE DOWNWIND LEG IN ORDER TO ALLOW SUFFICIENT SPACE BTWN OURSELVES AND THE TFC TO FOLLOW. WE WERE ABOUT TO TURN BASE WHEN LGA TWR TOLD US TO 'TURN L IMMEDIATELY TO A 040 DEG HDG.' I RPTED THAT WE WERE IN THE TURN; AND THE CTLR STATED THAT WE WERE ONLY 3 MI FROM JFK; APPARENTLY THE REASON FOR THE TURN. HE THEN ASKED US IF WE HAD THE TFC IN SIGHT; AND I RESPONDED THAT WE DID. THE SPACING LOOKED GOOD AT THIS TIME AND WE WERE RECLRED FOR THE VISUAL APCH TO RWY 31. WE CONTINUED AND LANDED ON RWY 31. I BELIEVE THAT LGA APCH AND TWR PROVIDED INADEQUATE SEPARATION BTWN US AND OUR PRECEDING TFC. FIRST THEY CLRED US FOR THE VISUAL APCH; THEN THEY GAVE US A HDG TO FOLLOW TFC; THEN CLRED US TO FOLLOW TFC; THEN GAVE US A HDG BECAUSE WE WERE TOO CLOSE TO JFK; THEN CLRED US FOR THE VISUAL. WHEN THEY CLRED US FOR THE VISUAL BEHIND TFC; WE (THE CREW) WERE RESPONSIBLE FOR SEPARATION. WE DECIDED WHEN WE HAD ENOUGH ROOM TO FOLLOW; BY GIVING US HDGS AND CLRING US VISUALLY; LGA IS TRYING TO 'HAVE IT BOTH WAYS;' AND ATTEMPT TO PROVIDE SPACING BUT GIVING THE MAIN RESPONSIBILITY TO THE COCKPIT CREW. IN THE CONGESTED AIRSPACE OVER NEW YORK; LGA NEEDS TO HAVE MORE POSITIVE CTL OVER ACFT SPACING. PERHAPS ASSIGNING SPDS AS WELL AS HDGS IN ORDER TO ASSURE SPACING IS SOMETHING THEY COULD CONSIDER. ALSO; IF THEY WOULD PUT THE APCH IN USE ON THE ATIS; THIS WOULD HELP CREWS TO BE BETTER PREPARED FOR THE APPROPRIATE ARR. LGA APCH SHOULD DO A BETTER JOB OF PROVIDING SEPARATION OF ACFT BEFORE ACFT ARE OPERATING IN THE TFC PATTERN. IT WOULD BE MUCH BETTER TO HOLD ENRTE OR EVEN DELAY DEPS ENRTE TO LGA TO ACHIEVE SEPARATION EVEN IF IT MEANS DELAYS TO LGA.