A Vehicle Stability Study of Combined Alignments on Mountainous Freeways: A Driving Simulator-Based Approach

Vehicle stability is important for ensuring road safety. Shown in previous studies, crash risks on freeways were closely associated with vehicle stability, especially when passing a horizontal curve. Claimed dangerous, combined horizontal and vertical alignments are used frequently in mountainous freeways. Some studies have provided the relationship between road alignment and vehicle stability, but they involved the 85th percentile value or average value of all the drivers, which ignores the difference between individuals. In this study, combined alignments implemented in a driving simulator were classified into four types. Lateral offset and lateral acceleration were investigated on individual levels. The influence of combined alignment on vehicle stability was analyzed using random effects logistic regression models. The models showed that the slope, curvature, length, and turn direction had significant influence on vehicle stability. For different types of combined alignments, the significant influence characteristics were different.