Mental Workload as a Function of Traffic Density: Comparison of Physiological, Behavioral, and Subjective Indices

Baldwin, Carryl L; Coyne, Maria T · 2003 · Crossref

DOI: 10.17077/drivingassessment.1084

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Summary

This study investigates how traffic density affects driver mental workload and compares the sensitivity of physiological, behavioral, and subjective assessment methods. Motivated by the high prevalence of driver inattention in crashes and the increasing complexity of in-vehicle technologies, the research aims to establish effective methodologies for measuring attentional demands in driving environments. Specifically, it evaluates whether analogous visual and auditory sensory detection tasks can reliably assess workload changes induced by varying traffic conditions. The experiment utilized a dual-task paradigm with seven licensed drivers operating a GE Capital I-Sim driving simulator. Participants performed simulated driving under low and moderate traffic density conditions while simultaneously completing visual or auditory oddball detection tasks. The visual task required identifying red target colors among green distractors, while the auditory task involved distinguishing 1000 Hz target tones from 1500 Hz distractors. Mental workload was assessed using three indices: physiological measures via P300 event-related potential (ERP) amplitude recorded from EEG electrodes; behavioral measures including response time (RT) and accuracy on the detection tasks; and subjective ratings using the NASA Task Load Index (TLX). The results revealed distinct sensitivities across the three assessment methods. Behavioral measures proved highly sensitive to traffic density; both response times and accuracy on the detection tasks significantly deteriorated as traffic density increased from low to moderate levels. However, no significant differences were found between visual and auditory modalities in these behavioral metrics. In contrast, P300 amplitude, while significantly larger for targets than distractors during baseline trials, failed to show a statistically significant change in response to increased traffic density, likely due to low statistical power and high individual variability. Subjective TLX ratings indicated that driving alone was perceived as less difficult than dual-task conditions. Furthermore, participants rated the combination of driving with the visual detection task as significantly more difficult than driving with the auditory detection task, a distinction not captured by the behavioral or physiological measures. The study concludes that no single metric fully captures the multidimensional nature of mental workload. Behavioral performance measures were effective in detecting increased task demands from traffic density, while subjective ratings were necessary to identify modality-specific difficulties, particularly the higher perceived burden of visual secondary tasks. The findings underscore the importance of employing a multi-method assessment approach to accurately model and evaluate driver workload in surface transportation environments, especially when comparing the impact of visual versus auditory in-vehicle displays.

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Topics

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• workload measurement
• mental demand
• stress driving
• neuro workload indices
• road complexity
• traffic density

Information type

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• Empirical Findings: physiological data
• Methodological Resource: validation psychometrics
• Theoretical Contribution: theory or model