WHILE DRIVING TO A BOOK STORE, A STEERING INPUT WAS MADE TO AVOID A TRACTOR IN THE ROAD. AT THIS POINT THE VEHICLE BECAME COMPLETELY UNCONTROLLABLE, UNRESPONSIVE TO ANY AND ALL FURTHER INPUTS.THE VEHICLE DEPARTED THE ROAD CROSSING A MEDIAN, TWO NORTHBOUND LANES OF TRAFFIC, UP A BANK AND ROLLED AT LEAST 2 TIMES BEFORE STOPPING. INSPECTION OF THE STEERING LINKAGE INDICATED FAILURE OF THE STEERING BOX SHAFT WHERE THE CONTROL ARM ATTACHES TO THE STEERING BOX. THIS FAILURE MAY HAVE OCCURRED DURING THE INITIAL STEERING INPUT. ADDITIONALLY, THE CONTROL ARM WAS BENT TOWARD THE REAR OF THE VEHICLE, POSSIBLY INDICATING IT HAD BEEN DRAGGED FOR MOST IF NOT ALL OF THE MISHAP.