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Certain multiply-articulated truck combinations are known to exhibit lightly damped trailer yaw motions in response to rapid inputs of steering. This paper clarifies the yaw response phenomenon and illustrates this characteristic for ten vehicle combinations which are currently in use in the U.S. The phenomenon of interest is described in terms of the “amplification” in lateral acceleration level experienced at the rear-most trailer of the combination with respect to the lateral acceleration level achieved at the truck or tractor. Results from two types of computerized simulation are presented; one representing a linear treatment of the vehicle and producing frequency response characteristics, and the other representing a rather complete nonlinear treatment of the vehicle and producing time history responses in an emergency obstacle-avoidance maneuver.

The roll stability of heavy-duty trucks and truck combinations is discussed both on the level of the fundamental mechanics of vehicle response and from the viewpoint of the quantitative influence of size and weight variables. The presentation on fundamentals begins with the case of a rigidly-suspended vehicle and builds up to the case of a tractor-semitrailer with distinctive suspension stiffnesses and spring lash properties at the various axle positions. Size and weight considerations cover variations in axle load, gross weight, and overall width as well as incidental issues involving the height and possible lateral offset of the payload center of gravity. Size and weight influences on roll stability are interpreted in terms of the likely implications for rollover accident involvement.

Rollover accidents are of special concern for commercial vehicle safety. The relatively low roll stability of the commercial truck promotes rollover and contributes to the number of truck accidents and injuries. This Research Report takes an in-depth look at the mechanics and contributing factors to rollover accidents and helps to identify prevention strategies.