DRIVER PROCEEDING ALONG INTERSTATE AT 60 MPH WITH CRUISE ENGAGED WHEN FELT A JOLT IN REAR END AND TRUCK STARTED FISHTAILING. TRUCK STRUCK SIDE BARRIER, SPUN, CROSSED 3 TRAFFIC LANES AND CAME TO STOP. RIGHT REAR WHEEL ASSEMBLY WAS DETATCHED AND HAD COME TO REST ALONG SHOULDER. SUBSEQUENT DEPARTMENT MECHANIC INSPECTION REVEALED WHAT APPEARS TO BE SHEARING OF AXLE, WITH CENTER OF AXLE APPEARING POROUS. *AK