I am willing to bet he had a lead axle brake malfunction and overheat, touched his brake pedal and the DOT mandated brake override system applied all the tractor brakes to the max the ABS would allow. He would then have about a 20 ton missile that was almost impossible to steer. Once he hit the dirt, the computer would have kept applying the tractor brakes to the max ABS permitted and he would have little or no steering ability with the trailers pushing from behind.