Safety evaluation of chevron markers and speed reduction markings for mountainous freeway combined alignments: a...

Mountainous freeways generally deploy safety countermeasures on crash-prone sections to mitigate crash risks from complex combined horizontal-vertical alignments, highlighting the importance of countermeasure evaluation in enhancing traffic safety. While international practices regarding safety improvements for crash-prone roadways have developed quantitative evaluation for implemented countermeasures, the specific design schemes of proposed countermeasures in the design stage usually rely on engineers combining engineering experience to make reasonable inferences based on design specifications, supplemented by crash features and cost-effectiveness. However, it is essential to validate the rationality of such proposed countermeasure design configurations (specifically for countermeasures involving complex driver-geometry interactions) before implementation, to provide quantitative references for engineers to refine their schemes. Driving simulation is a powerful tool for this purpose, as it complements engineering inferences with behavioral-level quantification to validate and refine design schemes. Hence, this study developed a driving simulation-based framework for pre-implementation evaluation of chevron alignment markers and longitudinal speed reduction markings on seven combined alignment types within a 35 km crash-prone section of an operational mountainous freeway in China. Using the high-fidelity Tongji University Driving Simulator, experiments involving 30 participants were conducted to collect vehicle operational data. Paired Wilcoxon signed-rank tests quantitatively evaluated effectiveness using five surrogate safety measures. Results revealed significant section-specific effectiveness: (1) Both countermeasures were most effective on curve-downgrade sections; (2) Neither significantly improved safety on curve-crest or curve-upgrade sections; (3) Both countermeasures were particularly effective for sections with R_H < 2500 m, G < |2.0| %, and ΔG ≥ |2.0| %. These findings provide quantitative guidance for engineers to refine section-specific design schemes and resource allocation during the planning stage, ensuring safety countermeasures customized for the unique demands of different combined sections.