Combined horizontal and vertical alignments are frequently present in mountainous freeways. These complex geometric alignments prompt drivers to adjust their speeds frequently. Speed changing at considerable rates, particularly deceleration, may indicate reduced driving comfort and even cause potential safety risks. The primary objectives of the presented study were: 1 to investigate which geometric design characteristics have significant influence on deceleration and acceleration, and 2 to help engineers design alignments that promote smooth operating speed profiles and, thus, safer driving. The Tongji driving simulator was used to expose subjects to roadway conditions typical for a freeway designed for a mountainous terrain. The speed changes of drivers were measured every five meters and then classified as deceleration, near-cruising, and acceleration. Since an individual driver’s deceleration and acceleration are correlated, a random effects multinomial logistic regression model was used to reflect the relationship between road alignment and acceleration and deceleration. The model showed that the grade of combined alignment segment, tangent-proportion of the following 400 meter segment, and maximum slope change of the preceding 400 meter segment had significant effects on deceleration and acceleration. Various graphs were developed to show the effect of combined alignments on the deceleration and acceleration probabilities.
Xuesong Wang*, Jiao Liu, Tarko A P, Rongji Yu, Xiaohan Yang. Effects on Deceleration and Acceleration of Combined Horizontal and Vertical Alignments on Mountainous Freeways: A Driving Simulator Study, Transportation Research Board 96th Annual Meeting, Washington D.C., USA, 2017. 1.8-12.
Effects on Deceleration and Acceleration of Combined Horizontal and Vertical Alignments on Mountainous Freeways A Driving Simulator Study.pdf