This paper describes an investigation that was undertaken to evaluate the lateral forces and moments produced on a vehicle with large, flat lateral faces when it is passing or being passed by a large vehicle in an adjacent traffic lane. The forces and moments were determined from tests that were conducted in the University of Tennessee subsonic wind tunnel. They were, then, input to a computerized vehicle model to find the resulting dynamic response of the vehicle. These forces and moments were sufficiently strong to produce a significant lateral deviation from the desired path of the vehicle. Resulting from this investigation, several recommendations were made to improve highway safety.