Evaluating Alignment Consistency for Mountainous Expressway in Design Stage: Driving Simulator-Based Approach

Evaluating design consistency is of great significance for safety evaluation on roadway design prior to its construction. Conventional design consistency showed little consideration of driving performance due to the limitation in data availability. More importantly, they were performed only on the existing roads. In this study, a simulated driving experiment was carried out in a high-fidelity driving simulator in Tongji University (Shanghai). A design stage four-lane (two-ways) mountainous expressway was implemented geo-based on the basis of the detailed road design blueprint. We attempted to establish a practical approach for evaluating its design consistency through investigating operating speed consistency, vehicle stability and vehicle lateral offset (vehicle trajectory). Specifically, the speed consistency is studied using the classic indicators ¨C the 85th speed reduction and 85th maximum speed reduction. The vehicle stability was evaluated using lateral acceleration, rollover coefficient and the conventional side-friction parameter. In the lateral offset analysis, the adjusted lateral offset was newly proposed, which is defined as the lateral offset from ideal vehicle trajectory. Utilizing the adjusted lateral offset can reflect the trajectory variation dependent on the characteristics of road geometry, which leads to the discovery of the inconsistencies in the studied mountainous expressway. The lateral acceleration and rollover coefficient could be considered as supplementary measures to provide insights into drivers’ comfortableness as well as the rollover risk. Another contribution of this work is that we developed predicting models for the considered consistency measures. The purpose is to better understand the relationship between driving performance and roadway geometry characteristics, as well as to provide a practical formulation in a rigorous manner for road design consistency evaluation.