Effects of Horizontal‐Curve Transition Design on Truck Roll Stability

The intent of this article is to provide information that will facilitate the design of roads that are safer for heavy trucks, which have a greater tendency to roll over than passenger cars. The roll performance of tractor‐semitrailer trucks on horizontal curves with three different types of transitions is investigated using computer simulation, and the results are used to develop guidelines for horizontal‐curve transition design. The roll dynamics of a truck traveling on a transition and a superelevated curve are described, and the effect of superelevation on the rollover threshold of tractor‐semitrailer trucks is also discussed. Three evaluation parameters (roll stability margin, acceleration overshoot, and critical speed) are proposed and used in evaluating different transition types. Three types of transition are investigated: one in which 2/3 of the maximum superelevation is developed before the start of the curve; one in which the superelevation is fully developed at the start of the curve; and one in which superelevation is developed in a short spiral section. A test matrix consisting of different truck speeds, different radius curves, and different transitions is used. The spiral transition is shown to be most desirable type of transition.