The consequences of an increase in heavy goods vehicles for passenger car drivers’ mental workload and behaviour: A simulator study

de Waard, Dick; Kruizinga, Anje; Brookhuis, Karel A. · 2008 · Crossref

DOI: 10.1016/j.aap.2007.09.029

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Summary

This study investigates the impact of a projected 70% increase in Heavy Goods Vehicles (HGVs) on passenger car drivers’ mental workload and driving behavior, motivated by concerns that HGV columns will increase congestion, reduce visibility, and elevate accident risks. Using a driving simulator, the researchers examined how increased HGV density affects merging into traffic and exiting motorways, specifically testing hypotheses regarding mental effort, safety margins, visibility obstruction, and lane-changing behavior. The experiment involved 42 licensed drivers (32 experienced, 10 inexperienced) in a within-subjects design. Participants drove through three traffic conditions: private cars only, a mixed traffic scenario (2006 baseline), and an HGV column scenario (950 HGVs/hour in the slow lane). Two visibility conditions (clear and fog) were also tested. Data were collected via driving performance metrics (speed, lateral position, time-headway, time-to-collision), physiological measures (heart rate and heart rate variability), subjective self-reports (mental effort, risk, annoyance), and observed behaviors (merge location, missed exits). Results indicated that merging into traffic with an HGV column required significantly more mental effort and was perceived as riskier than other conditions. Drivers exhibited greater speed variation and shorter minimum time-headways (safety margins) when merging, particularly when joining in front of an HGV. While physiological heart rate increased during merge decisions, heart rate variability in the HGV column condition showed unexpected increases, which the authors interpret as potential driver resignation or strategy change rather than reduced effort. Regarding exits, drivers missed exits more frequently in the HGV column condition due to blocked signage, though they did not change lanes earlier to compensate. Fog conditions led to slower speeds and more missed exits but did not significantly alter headway safety margins. Inexperienced drivers maintained safer headways than experienced drivers. The study concludes that increased HGV presence makes merging more demanding and less safe, characterized by reduced safety margins and higher cognitive load. The obstruction of exit signs by HGV columns leads to missed exits, suggesting a need for overhead signage or navigation aids. The authors warn that these increased task demands may disproportionately affect elderly drivers and recommend Advanced Driver Assistance Systems, such as blind spot detectors, to mitigate risks associated with future traffic compositions.

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Topics

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• traffic density
• mental demand
• stress driving
• work zones

Information type

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• Empirical Findings: physiological data, behavioral performance data
• Theoretical Contribution: theory or model