B727 SO CONCERNED WITH VAGUE TWR TAXI INSTRUCTIONS. ACFT IS FORCED TO REVERSE COURSE WHEN TAXI BARRICADES ARE OBSERVED. SO BELIEVES DETAILED TAXI INSTRUCTIONS ARE REQUIRED.

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AFTER LNDG ON RWY 4L AT JFK ARPT IN NEW YORK; ATC INSTRUCTED US TO TAXI TO THE RAMP VIA RWY 31R. ACCORDING TO THE ARPT NOTAMS RWY 31R WAS CLOSED TO TKOF AND LNDG BUT OPEN FOR TAXIING ACFT. AS WE APCHED OUR TURNOFF AT THE DEP END OF RWY 31R; WE NOTICED A VEHICLE ON THE TXWY WITH BARRICADES BEHIND IT. SINCE WE WERE UNABLE TO TAXI THIS WAY; THE CAPT DECIDED TO TURN THE ACFT AROUND ON THE RWY AND GO BACK TO THE PREVIOUS OPEN TURNOFF. AS THE ACFT WAS HALFWAY THROUGH THE TURN WE HEARD AND FELT A THUMP ON THE NOSE GEAR. AFRAID THAT WE MIGHT HAVE CLIPPED A TXWY LIGHT; WE NOTIFIED ATC ABOUT THIS. AS WE WERE CONTINUING OUR TAXI; WE COULD NOT DETERMINE IF IT WAS A LIGHT WE STRUCK OR JUST A BUMP IN THE PAVEMENT. THE REST OF THE TAXI WAS UNEVENTFUL. AFTER GETTING OUT OF THE ACFT WE COULD NOT FIND ANY DAMAGE WHATSOEVER TO THE NOSE GEAR TIRES. I BELIEVE ATC SHOULD HAVE GIVEN US MORE DETAILED TAXI INSTRUCTIONS AND INFORMED US OF THE TXWY CLOSURE. IN THE FUTURE; I BELIEVE THE FLC SHOULD ALWAYS ASK FOR COMPLETE TAXI INSTRUCTIONS; IF NOT SURE OF WHAT RTE ATC INTENDED FOR US TO PROCEED ON.