Stress and Fatigue Effects of Driving Longer-Combination Vehicles

NHTSA · 2000 · ROSA P / United States. Federal Motor Carrier Safety Administration

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Summary

This study, sponsored by the Federal Motor Carrier Safety Administration (FMCSA) and conducted by the Battelle Human Factors Transportation Center, investigates the stress and fatigue effects of operating longer-combination vehicles (LCVs). Motivated by Section 4007(d) of the Intermodal Surface Transportation Efficiency Act of 1991, the research aimed to determine if LCVs significantly increase driver stress and fatigue compared to standard single tractor-trailer vehicles. The study focused specifically on fatigue under normal operating conditions rather than general vehicle safety. The experimental design involved 24 experienced commercial drivers, aged 40 to 62, who drove approximately 2,700 miles each over seven consecutive days. Participants alternated between three vehicle configurations: a single 48-foot trailer, a triple-trailer combination with standard fixed-axle converter dollies (A-dollies), and a triple-trailer combination with self-steering double-drawbar converter dollies (C-dollies). Data collection included subjective measures via standardized questionnaires (Stanford Sleepiness Scale, NASA Task Load Index) and objective measures including physiological data (heart period), performance tests (reaction time, motor coordination), and driving metrics (lane deviation, steering corrections). The results demonstrated statistically significant differences in fatigue and workload across configurations, following a consistent pattern where A-dolly triples induced the highest stress, C-dolly triples induced intermediate stress, and single trailers induced the lowest. Specifically, driving A-dolly configurations resulted in cautionary-to-red-line workload levels and significantly increased lane variability. Crucially, the study identified "carryover effects," where fatigue and performance degradation persisted into the following day. Drivers exhibited high carryover fatigue and increased workload the day after driving A-dolly triples, whereas those driving single trailers showed positive recovery. C-dolly drivers experienced neutral carryover effects. The findings conclude that triple-trailer drivers maintain a higher probability of safe operation when using Super C-dolly configurations compared to standard A-dolly configurations. The study highlights that individual driver differences account for 32 to 51 percent of variance in performance, suggesting that some drivers are more challenged by the task. These results imply that vehicle configuration significantly impacts driver alertness and safety, supporting the use of self-steering dollies to mitigate fatigue-related risks in LCV operations.

Key finding

Triple-trailer configurations with standard A-dollies resulted in significantly higher driver fatigue and workload than single trailers or C-dolly configurations, with fatigue carryover effects persisting into the following day.

Methodology

simulator

Sample size: 24

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified_with_issues.

Topics

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• truck driver fatigue
• time on task
• drowsiness

Information type

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• Empirical Findings: physiological data
• Theoretical Contribution: theory or model