Investigation of vehicle motion on sharp horizontal curves combined with steep longitudinal grades

The research addresses the safe negotiation of sharp horizontal curves combined with steep longitudinal grades. Instrumented field measurements were carried out utilizing a FWD C-Class passenger car in both upgrade and downgrade directions of travel. Initially, the vehicle was driven in braking mode on adjacent steep grade tangent sections in order to define the peak friction coefficients. During vehicle’s tractive mode, for various speed values, friction data were measured and correlated against a vehicle dynamics model developed by the authors’ as well as the point mass model, in order to examine the interaction between vehicle dynamics and road geometry in such alignments. The findings regarding vehicle speed prediction revealed that the dynamic model, on both upgrades and downgrades, is accurate. On the other hand, the point mass model although more simple, revealed accuracy, of a smaller degree, however, but only on upgrades. Moreover, certain findings are reported among which the fact that steep upgrades are more critical at impending skid conditions as well as the acceleration impact in vehicle’s safety.