PA28 PLT HAS FUEL STARVATION DURING CRUISE AND EXECUTES AN OFF FIELD LNDG.

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FLT PLANNING AND STANDARD WX BRIEFING WITH FORECAST OF WINDS AT OUR CRUISING ALT USED IN OUR CALCULATIONS; SHOWED WE SHOULD HAVE UP TO 2 EXTRA HRS OF FUEL PAST OUR REFUELING POINT; AT ECONOMY CRUISE. WE ENCOUNTERED TURB AND INCREASED HEADWINDS BEYOND PREDICTIONS AND SOME WINDSHEAR . AT OUR LAST CHK POINT; A VOR NEAR AN ALTERNATE ARPT WITH FUEL; I DECIDED TO GO ON BASED ON A FUEL GAUGE READING; THAT SEEMED TO BE RIGHT BASED ON FUEL BURN FOR ECONOMY CRUISE SPDS. THE PLANE RAN OUT OF FUEL 4 MI E OF THE ARPT; AND WE DIDN'T HAVE ENOUGH ALT TO GLIDE TO THE ARPT. WE LANDED ON A HWY JUST OUTSIDE OF TOWN; WITH NO DAMAGE AND NO INJURIES TO ANYONE! FACTORS: 1) TURB COMBINED WITH EFFORTS TO MAINTAIN ALT BURNED FUEL AT A FASTER RATE. 2) A STICKING FUEL GAUGE NEEDLE GAVE A FALSE READING; WE COULD HAVE LANDED AT A CLOSER ARPT; IF THE GAUGE READ RIGHT. FUTURE: 1) ADD '1/3 PLUS' TO THE BURN RATE CALCULATIONS WHEN MODERATE TURB IS ENCOUNTERED. 2) DON'T TRUST GAS GAUGES; ONLY TRUST TIME AT BURN RATE AND ADD IN 1/3 FACTOR FOR TURB; AND 3) REALLY MONITOR GND SPDS.