FLT INSTRUCTOR WITH STUDENT PLT HAS CLOSE ENCOUNTER WITH GND VEHICLE XING RWY WITH NO COM. GAR EXECUTED.

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WE WERE OPERATING OUR ACFT IN THE TFC PATTERN AT C83; PRACTICING LNDGS. ALL CORRECT RADIO COMS WERE CONDUCTED ON THE CTAF FREQ AND THE ACFT ANTI-COLLISION LIGHTS AND LNDG LIGHTS WERE ILLUMINATED. ON FINAL APCH; AS THE ACFT ARRIVED AT THE THRESHOLD; A VEHICLE WAS NOTICED ON A TXWY; N OF THE RWY. THIS CITY VEHICLE WAS PROCEEDING AT A RAPID RATE (AROUND 30 MPH ESTIMATED) TOWARD RWY 23 ON AN INTERSECTING TXWY THAT CROSSED RWY 23 ABOUT 1000 FT DOWN. AS THE VEHICLE APCHED THE RWY; I CONSIDERED THE FACT THAT IT MIGHT PROCEED ONTO AND CROSS THE RWY; BUT I ASSUMED THAT IT WOULD TURN AND PARALLEL THE RWY AND NOT BE A COLLISION HAZARD. THE VEHICLE; HOWEVER; PROCEEDED RIGHT ONTO THE RWY JUST AS WE BEGAN TO REDUCE PWR FOR LNDG. I INITIATED A GAR AND AT THE SAME TIME THE DRIVER OF THE VEHICLE SAW US AND TOOK EVASIVE ACTION. THE VEHICLE CONTINUED S OVER THE EDGE OF THE RWY AND CRASHED IN A DITCH. MY GAR WAS SUCCESSFUL AND CONTACT BTWN THE AIRPLANE AND VEHICLE DID NOT OCCUR. AFTER A BRIEF PERIOD; THE DRIVER OF THE VEHICLE XMITTED ON THE CTAF FREQ AN APOLOGY FOR MAKING US GAR. HE STATED THAT HIS RADIO HAD BEEN OFF OF THE FREQ AND HE DIDN'T HEAR US COMING. NOBODY WAS INJURED. THIS OCCURRENCE BRINGS ABOUT 2 OBSERVATIONS; NEITHER NEW. FIRST; ACFT AND GND VEHICLES MUST BE VERY CAUTIOUS WHEN ENTERING A RWY. A VISUAL CHK OF THE FINAL APCH MUST ALWAYS BE MADE. I THINK THIS VEHICLE ASSUMED RWY 30 WAS IN USE SO DIDN'T VISUALLY CHK THE FINAL. SECOND; PLTS MUST EXERCISE EXTREME CAUTION IN LOOKING FOR POSSIBLE RWY INCURSIONS DURING LNDG. IF I HAD EXECUTED A GAR WHEN I FIRST SAW THE VEHICLE MOVING TOWARD THE RWY; THE MARGINS WOULD HAVE BEEN A LOT LARGER.