Safety Implications of Three-Dimensional Alignment Coordination in Highway Design: Sight Distance, Visual Perception, Design Methodologies, and Future Challenges

Highway geometric design standards provide some practical rules to achieve an appropriate three-dimensional (3D) coordination of the horizontal and the vertical alignment. When this coordination is not achieved, inadequate design outcomes may appear, such as hidden beginning of curves or sight-hidden dips, which could compromise traffic safety. However, other minor design flaws are not considered to entail a significant hazard. Based on the principles of visual perception, sight-distance analysis and the virtual creation of the highway perspective make it possible to detect and evaluate defects in design prior to construction, yet their systematic application has only recently been implemented. Several research works have addressed safety aspects of 3D alignment coordination either by estimating accident risk indirectly or by developing accident prediction models. This review synthesizes the current knowledge on defects in 3D alignment coordination and the available research on the safety implications of 3D alignment designs within the scope of sight distance and visual perception. The review focuses on methodologies that integrate advanced simulation tools and statistical models to evaluate the safety implications of geometric design features. ... mehrIn addition, it analyzes how geometric design guidelines address issues of poor 3D alignment coordination and identifies future challenges in this area of knowledge.