Lane departures represent a serious safety concern since they are responsible for a substantial number of motor vehicle crashes. Existing studies indicate that vertical and horizontal alignments (i.e. combined alignments) may be correlated with lane departures. There is, however, a dearth of research on how adjacent alignments in combination with combined alignments affect driving performances with respect to lane departures. Consequently, design guidelines that consider the safety impact of adjacent alignments are not currently available, especially in China. The objective of this paper is therefore to examine which geometric design characteristics (adjacent segments and/or combined alignments) have a significant influence on the probability of lane departure. With the aid of a 21 drivers driving simulator study of 24-km long two-way divided mountainous freeway, lane departure data were calculated for each 5-meter segment and classified into three categories of events: lane keeping, lane departure to the left and lane departure to the right. Since lane departure events by driver are correlated, a two-level multinomial logit model with random effects was employed to examine the contributory factors. Variables related to horizontal and vertical alignments on the current segment (i.e. combined alignment) and adjacent alignments (both upstream and downstream) were considered. The direction of a curve, vertical slope, the difference in horizontal curvatures (max-min) within the 300m adjacent upstream and the lane close to hard shoulder were all found to significantly influence lane departures. Average vehicle speed within the 300m adjacent upstream also had a significant influence on lane departure to the left. Horizontal curvature, on the other hand, was a significant variable for lane departure to the right. The research findings show that the optimum length of the adjacent upstream segment, which significantly influenced lane departure, is 300 m. Based on the findings, a further analysis was conducted to assist engineers in designing safer mountainous freeways.
Yixin Chen, Quddus M A, Xuesong Wang*, Rongji Yu, Ang Li. Impact of Combined and Adjacent Alignments on Lane Departure Using a Simulator Study, Transportation Research Board 96th Annual Meeting, Washington D.C., USA, 2017. 1.08-12.