Safety evaluation of freeway interchange merging areas based on driver workload theory

Prior safety evaluations of interchange merging areas have mostly focused on traffic conflicts and operating speeds, without considering how these factors can influence the driver workload. Researches regarding the level of driver workload have largely concentrated on urban roads, tunnel sections, and basic freeway segments, without considering the impact of merging traffic flows on safety. Therefore, this study has investigated how merging vehicles can impact through-driver workload and safety. Three independent field experiments were conducted on freeways, involving 18 drivers and 17 interchanges. The results showed that the vehicles merging onto freeway impact driver workload and driving performance, generating potential risk that cannot be ignored. Merging into the mainline traffic flow increases the through-driver workload to a higher level or even exceeds the safety threshold, despite there being better geometrical conditions of interchanges than those of basic freeway segments. When the volume of merging vehicles exceeds 564 pcu/h or the traffic saturation is above 0.485, driver workload rises above the safety thresholds and the driving risk is elevated, which potentially would lead to crashes. This study offers insights for more effective segment division of operating speed prediction, and dynamic risk management with regard to interchange safety.