How Tired is Too Tired to Drive? A Systematic Review Assessing the Use of Prior Sleep Duration to Detect Driving Impairment

Sprajcer, Madeline; Drew Dawson∥; Kosmadopoulos, Anastasi; Sach, Edward J.; Crowther, Meagan E.; Sargent, Charli; Roach, Gregory D. · 2023 · OpenAlex-citations

DOI: 10.2147/nss.s392441

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Summary

This systematic review addresses the persistent issue of driver fatigue, which contributes to approximately 20% of vehicle crashes. Unlike drink-driving, where clear legal limits for blood alcohol concentration have successfully reduced crash rates, fatigue-related crashes have not declined due to a lack of specific guidance on what constitutes "too tired to drive." The authors aim to establish an evidence base for the concept of "deemed impairment" based on prior sleep duration, identifying a specific sleep threshold below which drivers should be considered legally impaired. This approach seeks to provide clear public guidance and support enforcement strategies similar to those used for alcohol-related impairment. The study followed PRISMA guidelines, searching four online databases (PubMed, Web of Science, Scopus, and Embase) for peer-reviewed articles published between January 2000 and October 2021. Eligible studies involved human participants of legal driving age without sleep disorders and required measurements of prior sleep duration alongside driving performance indicators or crash outcomes. After screening 1,940 unique records, 61 studies were included in the qualitative synthesis. These comprised 21 experimental or quasi-experimental studies, 25 cross-sectional studies, 11 case-control studies, three naturalistic studies, and one longitudinal study. Experimental studies typically compared acute sleep loss against control conditions of habitual or recommended sleep (usually 7–9 hours). The findings indicate a dose-dependent relationship between prior sleep duration and driving impairment. Compared to well-rested individuals (≥8 hours of sleep), those with 6 or 7 hours of prior sleep exhibited a modest level of impairment, with crash likelihood increasing by approximately 30%. Significant decrements in driving performance occurred after one night of 4 or 5 hours of sleep, resulting in approximately double the likelihood of a crash compared to well-rested drivers. The review identifies a critical threshold where less than 5 hours of prior sleep leads to a notable decrease in performance and a substantial increase in crash risk. Experimental data further supported these findings, showing increased lane deviations, speed variability, and critical incidents following sleep restriction. The significance of this review lies in its potential to inform policy and public education regarding fatigued driving. By identifying specific sleep thresholds associated with measurable impairment, the authors provide a scientific foundation for establishing community standards and legal limits for "deemed impairment." This could enable the implementation of deterrence strategies, such as prosecution for driving with insufficient prior sleep, mirroring the success of blood alcohol concentration limits. The study concludes that defining a minimum sleep requirement is a critical step toward reducing fatigue-related crashes and improving road safety.

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Topics

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• sleep deprivation
• time on task
• truck driver fatigue
• drowsy as impairment
• drowsiness
• circadian factors