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

Area of Science:

• Traffic Engineering
• Human Factors in Transportation
• Road Safety Analysis

Background:

• Previous safety assessments of freeway interchanges primarily focused on traffic conflicts and speeds, neglecting driver workload implications.
• Existing driver workload research is concentrated on urban roads, tunnels, and basic freeway segments, overlooking the safety impact of merging traffic.
• The influence of merging traffic flows on driver workload and safety at interchanges remains under-investigated.

Purpose of the Study:

• To investigate the impact of merging vehicles on the workload and safety of through-drivers on freeways.
• To identify critical thresholds for merging vehicle volume and traffic saturation that elevate driver workload and safety risks.

Main Methods:

• Conducted three independent field experiments on freeway segments.
• Involved 18 drivers and data collection across 17 interchanges.
• Analyzed driver workload and driving performance in relation to merging traffic conditions.

Main Results:

• Merging vehicles demonstrably increase through-driver workload and negatively affect driving performance, posing significant safety risks.
• Driver workload exceeds safety thresholds even with favorable interchange geometry when merging traffic is present.
• Elevated driver workload and increased driving risk, potentially leading to crashes, occur when merging vehicle volume surpasses 564 passenger car units per hour (pcu/h) or traffic saturation exceeds 0.485.

Conclusions:

• Merging traffic is a critical factor influencing driver workload and safety at freeway interchanges.
• The study provides crucial data for refining operating speed prediction models and implementing dynamic risk management strategies for interchange safety.
• Findings highlight the need to consider merging traffic dynamics in the design and management of freeway interchanges to ensure driver safety.