A metallurgical and mechanical failure analysis was applied as part of a vehicle accident reconstruction of a multi-vehicle collision. One of these vehicles was a coal hauling tractor-trailer. Examination of the trailer involved in the incident revealed a fatigue fracture to a primary lateral stiffener, along with a significant misalignment of the stiffener. Stress and fatigue analysis indicated that the misalignment severely degraded the fatigue life of the stiffener. Evaluation of the structural dynamics of the trailer after the fatigue fracture indicated decreased lateral stability. The decreased stability allowed by fracture of the lateral stiffener allowed for rollover of the trailer to occur while negotiating a curve. The failure sequence developed in this investigation proved consistent with all physical damage observed on the trailer and with witness accounts of the incidents. The failure scenario developed in this investigation is compared with other conclusions made by other investigators. It is shown that those conclusions are not consistent with all of the available evidence.