RWY AT CRW ARPT WAS OCCUPIED BY A SNOW SWEEPER WHEN A REGIONAL JET CHKED IN ON A 1 MI FINAL.

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I WAS WORKING THE LCL CTL POS AT CRW; WV; ON JAN/XA/01. VISIBILITY WAS RESTR DUE TO SNOW SHOWERS AND LOW CEILINGS. A VEHICLE WAS ON THE MAIN RWY (RWY 5/23) TRAVELING SWBOUND SWEEPING SNOW. THE VEHICLE WAS APPROX 1500 FT FROM THE APCH END OF RWY 23 WHEN ACR X; A REGIONAL JET; FIRST CHKED IN. I GLANCED UP AT THE BRITE RADAR DISPLAY IN THE TWR AND WAS SHOCKED TO SEE THE ACFT ON A 1 MI FINAL TO RWY 23 AT 500 FT AGL. I LOOKED DOWN AT THE VEHICLE AND HE WAS 1000 FT FROM THE CLOSEST TURNOFF AND IT WOULD HAVE BEEN IMPOSSIBLE FOR HIM TO CLR THE RWY IN TIME FOR ACR X TO LAND. ACR X WAS SENT AROUND; BUT THE ACFT'S MOMENTUM ALLOWED THE ACFT TO DSND DOWN TO 200-300 FT AGL. ACR X OVER FLEW THE VEHICLE AT A LOW ALT. A REVIEW OF THE VOICE TAPES INDICATED THAT ACR X WAS NEVER ADVISED TO CONTACT THE TWR BY APCH CTL. WHEN QUIZZED BY THE RADAR CTLR AFTER THE GAR THE PLT STATED HE SWITCHED OVER ON HIS OWN BECAUSE HE WAS 'COMING UP ON SHORT FINAL.' THIS SIT COULD HAVE BEEN TRAGIC IF ACR X HAD NOT SWITCHED FREQS ON HIS OWN. MORE OFTEN THAN NOT; PLTS LAND WITHOUT A LNDG CLRNC WHEN THEY ARE NOT SWITCHED TO THE TWR OR THEY FORGET TO CHANGE FREQ. THE POS AND DIRECTION OF THE VEHICLE; ALONG WITH THE LOW VISIBILITY; WOULD HAVE MADE IT DIFFICULT TO SPOT DURING LNDG. WE WERE WORKING WITH THE 'NEW' STAFFING LEVELS TODAY WHEN ACR X CAME WITHIN FT OF HITTING A VEHICLE. THE 4 CTLRS WERE WORKING THE 4 REQUIRED POS (2 IN THE TWR AND 2 IN THE RADAR ROOM) AND THE SUPVR WAS AWAY FROM THE OP DOING PAPERWORK.