Using Driving Simulators in Road Design–A Road Safety Study of Merging Traffic in Tunnels

Patten, Christopher JD · 2015 · Crossref

DOI: 10.4172/2165-7556.s3-014

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Summary

This study investigates road safety concerns regarding traffic merging from entry-ramp tunnels into the main Stockholm bypass tunnel, specifically focusing on the Lovö (1.5 km) and Vinsta (0.5 km) junctions. The research was motivated by the need to evaluate the safety of merging zones in long, curvy tunnels with steep descents, where drivers must judge speed and gap sizes under restricted sight lines. The authors addressed three primary questions: whether objective and subjective measures differed between the two ramp lengths, whether driver experience influenced merging performance, and how traffic intensity affected hazardous situations like late merging. The study utilized a driving simulator at the Swedish National Road and Transport Research Institute, replicating the planned geometry of the Stockholm bypass. Twenty-one participants with significant driving experience completed a 2x2x2 experimental design involving two entry-ramp lengths, two traffic gap sizes (1.5 seconds for dense traffic and 2.5 seconds for medium traffic), and two driver experience groups based on annual mileage. Participants drove through the tunnels and merged into the main tunnel, after which they rated their experience using the CR10 scale for mental demand, time pressure, frustration, and perceived risk. Objective data collected included distance-to-wall at merge completion, position between vehicles, time headway (THW) to forward and rearward vehicles, and mean speed. The results indicated that merging zones were insufficient for safe and comfortable merging for some drivers, particularly in the shorter Vinsta ramp under dense traffic conditions. More than 25% of drivers in the Vinsta condition with 1.5-second gaps completed the merge with less than two seconds of THW remaining before the end of the tapered section, a threshold considered the bare minimum for safety. Statistical analysis revealed significant main effects of gap size on distance-to-wall, position-between-vehicles, and THW measures, but no significant effects of ramp length or driver experience on most objective metrics. Subjectively, dense traffic (1.5-second gaps) significantly increased mental demand and perceived risk compared to medium traffic. Four participants experienced rear-ended collisions during the simulation, all occurring in the dense traffic conditions. The findings suggest that the current design of the merging zones, particularly the short Vinsta ramp, poses safety risks when traffic is dense, as drivers are forced to merge with insufficient time headway. The study highlights the utility of driving simulators in identifying such infrastructure flaws before construction. It implies that road design must account for realistic traffic intensities and that merging zones may need to be extended or redesigned to ensure drivers have adequate space and time to merge safely, thereby reducing the likelihood of hazardous situations and collisions in tunnel environments.

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Topics

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• gap acceptance
• traffic density
• following distance
• perceptual countermeasures

Information type

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• Empirical Findings: behavioral performance data
• Methodological Resource: tool software, validation psychometrics