Combined horizontal and vertical alignments are frequently used in mountainous freeways, but there is little quantified analysis of them for application in current design regulations and standards. This study develops a method to evaluate the safety of combined alignments, using speed differential as the indicator of safety. A simulated driving experiment was carried out in a high-fidelity driving simulator. Combined alignments were classified into four types (upslope-curve, downslope-curve, crest vertical curve-curve and sag vertical curve-curve), and four Random Effects Logistic Regression models were established. Various geometric characteristics were adopted as independent variables, including the average grade, radius, curvature change rate, length of the curve and so on. The models showed that slope, curvature, length and turn direction had significant influence on vehicle stability.
Jiao Liu, Xuesong Wang*. Safety Evaluation of Combined Alignments of Freeway: a Driving Simulator Study, The 14th World Conference on Transport Research, Shanghai, China, 2016.7.10-15.
Safety Evaluation of Combined Alignments of Freeway：a Driving Simulator Study.pdf