Rear differential or axle suffered catastrophic failure on highway, causing both rear wheels to lock up and the driveshaft to shear off/separate from the differential housing. Locking rear wheels at 55mph caused the vehicle to lose traction and spin out. Vehicle crossed multiple lanes of interstate highway, colliding with a snow bank facing the wrong direction. Fortunately traffic was light (incident occurred approx. 5:30AM on Sunday) and snow prevented the vehicle from colliding with the median wall. Had the incident occurred at another time or another place, injuries or fatalities would have been considerably more likely. Only advance warning was approx. 5 seconds of loud noise and intense vehicle shuddering from the rear before the wheels locked and control was lost. Once traction was lost, multiple driver-assist indicators lit up, but shut off after motion stopped. Vehicle was immobilized afterwards and had to be 'shaken' off the tow truck as the rear wheels would not turn. New vehicle, approx. 4,000 miles. Vehicle is currently at the local Ford dealership awaiting inspection.