Effects of Cellular Telephone Use on Driver's Mental Workload while Car Following

Tokunaga, R. A.; Nonami, K.; Hagiwara, T.; Kagaya, S.; Shimojo, A. · 1999 · Crossref

DOI: 10.2208/journalip.16.895

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Summary

This study investigates the impact of cellular telephone use on drivers' mental workload during car-following maneuvers on a real expressway. Motivated by concerns that secondary tasks like phone use increase accident risk, the research aims to quantify this danger by analyzing both objective reaction times and subjective mental workload. While previous studies often relied on simulators or focused on hand-held devices, this experiment utilized a hands-free system in actual driving conditions to assess whether experience with phone use mitigates cognitive load. The experimental design involved 16 male civil engineers with varying levels of experience using cell phones while driving. Participants drove a following vehicle on the Dōō Expressway in Japan, maintaining a constant 50-meter distance behind a lead vehicle. The study compared three conditions: car-following only, phone operation (dialing/receiving), and phone conversation. Mental workload was measured using two metrics: objective reaction time, defined as the interval between the lead vehicle’s brake light illumination and the subject releasing the accelerator, and subjective mental workload, assessed via the NASA Task Load Index (TLX). Data were collected using laser radar, speed sensors, and video cameras. The results indicated that phone conversations significantly increased reaction times for both experienced and inexperienced drivers compared to driving alone. Experienced drivers’ reaction times increased from 0.44 seconds to 0.71 seconds, while inexperienced drivers’ times rose from 0.51 seconds to 0.71 seconds. However, subjective mental workload responses differed markedly by experience level. Inexperienced drivers reported significantly higher mental workload during phone tasks than during driving alone. In contrast, experienced drivers reported no significant increase in subjective workload; some even rated the phone conversation task as less demanding than driving alone. Statistical analysis confirmed a significant interaction between experience level and task type regarding subjective workload. The study concludes that while cellular phone use objectively impairs driver reaction times regardless of experience, it does not necessarily increase perceived mental workload for experienced users. This discrepancy suggests that experience may reduce subjective cognitive strain, potentially leading to overconfidence rather than improved safety. The authors note that the inability to distinguish between genuine reduced workload and overconfidence limits the safety implications, highlighting the need for further research under varied conditions to fully understand the risks associated with hands-free phone use.

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Topics

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• mobile phones
• mental demand
• workload measurement

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