AN ACR MLG REINED UP SHORT TO AVOID A VEHICLE ON THE RWY.

Narrative

AFTER BEING CLRED TO LAND ON RWY 4 AT LAGUARDIA ARPT AND EXECUTING A NORMAL ILS (FLOWN IN VMC). AS THE PWR WAS REDUCED TO IDLE IN THE TOUCHDOWN ZONE; THE CAPT NOTICED A VEHICLE OFF TO THE L SIDE OF RWY 4. AS THE MAIN GEAR CONTACTED THE RWY THE VEHICLE PROCEEDED ONTO THE RWY. THE VEHICLE (AN ARPT VEHICLE WITH A YELLOW FLASHING LIGHT) STOPPED ON THE RWY CTRLINE AND TURNED TOWARD THE ACFT; I LOWERED THE NOSEWHEEL ONTO THE RWY AND APPLIED MAX BRAKING AND NORMAL REVERSE THRUST TO INSURE THAT WE WOULD BE ABLE TO HOLD SHORT OF THE ARPT VEHICLE. SHORTLY AFTER I APPLIED MAX BRAKING AND NORMAL REVERSE THRUST; THE ARPT VEHICLE MADE AN ABRUPT R TURN AND EXITED RWY 4 TO THE W SIDE OF LAGUARDIA ARPT. AS WE CLRED RWY 4 ON GOLF TXWY; THE CAPT ASKED THE TWR ABOUT THE VEHICLE; TO WHICH THE TWR CTLR REPLIED THAT THERE WAS NO VEHICLE THAT HE OBSERVED ON RWY 4. SUPPLEMENTAL INFO FROM ACN 267191: THE VEHICLE WAS ON THE RWY FOR APPROX 3-5 SECONDS TOTAL AND WAS CLR OF THE RWY BEFORE THE ACFT CAME TO A STOP. BECAUSE RWY 13-31 WAS CLOSED; THE ACTIVITY OF VEHICLES WITH FLASHING LIGHTS WERE OBSERVED BUT WAS NOT A CONCERN DUE TO THE NOTAM. I FEEL OUR ACTIONS OF CONTINUING THE LNDG WITH MAX BRAKING WAS APPROPRIATE DUE TO THE VEHICLES' LOCATION. IF WE HAD ABORTED THE LNDG; WHICH WOULD HAVE RESULTED IN A TOUCH AND GO LNDG; THIS COULD HAVE PUT US IN A MORE DANGEROUS SIT BY PLACING THE ACFT CLOSER TO THE VEHICLE AT A HIGH RATE OF SPD.