Feeling Sleepy? Stop Driving—awareness Of Fall Asleep Crashes Part 3
Aug 21, 2023
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Notwithstanding the ideal scenario to avoid driving impairment entirely, noticing early signs of impairment may be useful to avoid extreme safety-critical events. Difficulty keeping to the center of the road and maintaining the correct speed each showed high accuracy in predicting a near-crash event (AUC: 0.88–0.81, respectively). However, while difficulty keeping to the center of the road was associated with a small increase in the odds of a lane deviation event, the capacity to accurately predict one of these events was limited. To date, there is a paucity of knowledge on the extent to which drivers (or non-drivers) can accurately reflect on their performance, and how this might change under conditions of sleep loss [40]. While Philip et al. reported that correlations between self-reported performance and actual driving performance were poor under conditions of sleep loss [32], performance monitoring was general, rather than specific. In contrast, and in line with our findings here, in our previous study of professional drivers undertaking a simulated drive following a night without sleep, difficulty maintaining speed and/or lane position was associated with actually increased variability in lane position and speed, and these symptoms had high accuracy for predicting severe driving impairment [17].
To support future recommendations of when to stop driving, we sought to develop thresholds of subjective ratings which predicted “early” (e.g. a single lane deviation) versus late (e.g. a near-crash event) signs of drowsiness. Reporting any signs of sleepiness (KSS of 6 or more) was associated with 3.5× increased odds of a lane deviation in the next 15 minutes, with 54% of adverse events detected, and a false positive rate of around 30%. Continuing to drive, such that the KSS increased to “sleepy, fighting sleep” (KSS ≥8), drastically increased the odds of a near-crash event, with a false positive rate of around 25% (although we note that the reported odds ratio is likely inflated (20.21) and thus we report the lower CI 95% of 2.43—see below). As drivers may not routinely employ a traditional KSS, education campaigns may wish to employ these two KSS descriptors as an increase in risk trajectory, that is, “some signs of sleepiness” being an early warning, with “sleepy, fighting sleep” suggesting more imminent danger.
We also report on the utility of specific symptoms, and advise drivers that “occasionally” reporting symptoms appear to better reflect earlier/moderate impairment (SSQ > 2/3), while “frequently” reporting them appear to reflect late/severe impairment (SSQ >4). We would therefore urge drivers to seek somewhere to stop and rest when feeling any signs of sleepiness, occasional signs of struggling to keep the eyes open, blurred vision, difficulty keeping to the center of the road, and nodding off to sleep. Once drivers feel they are “fighting sleep,” likely to fall asleep in the next five minutes, and/or reporting a “frequent” occurrence of these symptoms (in addition to mind wandering), driving should cease as soon (and as safe) as possible. With these recommendations in mind, future work should examine the accuracy of these predictors when presented as a dichotomous assessment in an independent test set comprising a large number of drivers, in ecologically valid (naturalistic) settings.
Our study findings should be interpreted with some considerations in mind. First, some of the analyses undertaken are affected by small sample sizes in observable events. Although our overall study sample (n = 16) was adequate (i.e. a recent systematic review of this topic area [awareness of sleepiness] demonstrated this sample size was the most common sample size to address this question, plus we had 95% power to detect a medium effect size), the reduced number of observations particularly for the threshold analyses (Tables 4 and 5) led to an OR which was imprecise (as indicated by the width of 95% confidence interval). We, therefore, took a cautious approach by reporting on those odds ratios where we had confidence of a medium effect size in predictive accuracy. Future work should expand the n and/or number of observations to provide more accurate estimates for easy-to-implement thresholds of self-reported sleepiness. Second, while we demonstrate high accuracy between sleepiness/sleepiness symptoms and adverse driving outcomes, inter-individual differences may be observed. For instance, previous studies, from our group and others, show individual variations in correlations between actual performance and subjective ratings of performance and sleepiness [41, 42]. These individual differences may be systematic, such that predictive accuracy may change as a function of the age or sex of the driver. While our study did include male and female drivers, and with a wide age range (19–65 years), we were not powered to specifically examine this and further work is required [14]. Third, we examined the association between subjective sleepiness/sleepiness symptoms and driving following one night without sleep, and this may be different for other sleep conditions, e.g. sleep restriction, chronic sleep loss, and extended duration work shifts. Additionally, our drive began 2 hours post night shift (due to transportation to the track/study set up), and thus may not directly apply to night shift workers driving home (although we have previously shown KSS immediately post-shift predicts subsequent self-reported driving impairment [6, 9]). While the association between subjective sleepiness and objective performance becomes more tightly coupled as sleep loss progresses (due to a stronger sleep signal) [41], the association is proposed to uncouple with chronic sleep loss [43]. Future work should therefore examine drivers’ awareness of sleepiness as an accurate predictor of driving impairment under a range of real-world conditions of sleep loss, including different sleep schedules, varied use of countermeasures, such as caffeine (noting that we controlled for caffeine to specifically examine the effect of shift work per se), and for different drive durations (we note that severe events accumulate relatively late in the drive compared to moderate events, which may underpin the strong association with increasing subjective sleepiness).
To summarize, we demonstrate that drivers are aware of sleepiness, and that subjective sleepiness and sleepiness symptoms predict adverse drowsiness events occurring in the next 15 minutes, particularly those events considered severe (near-crash event, JDS4.5+). The overall best subjective predictors included the KSS, self-reports relating to eye symptoms (struggling to keep the eyes open, vision becoming blurred), and those relating to driving performance (particularly difficulty staying in the middle of the road). We note that the subjective ratings that best match the objective outcome appear to be the most ideal (e.g. subjective ocular predicting objective ocular [JDS], subjective driver behavior predicting actual driver behavior, and LFA/nodding off predicting microsleep events). A task force led by the National Highway Traffic Safety Administration (NHSTA) identified a comprehensive set of strategies to end drowsy driving crashes and related serious injuries and deaths. Public awareness, behavior, and education were identified as key factors [44], and our data are critical for informing these interventions. We recommend that drivers should routinely assess how sleepy they feel, and any associated sleepiness symptoms. Drivers should find a safe place to stop and take remedial action if they report (1) any signs of sleepiness (nonspecific, KSS greater than 6), and (2) any “occasional” experience of the following (specific) symptoms: struggling to keep the eyes open, blurred vision, nodding off, and/or difficulty keeping to the center of the road/maintaining the correct speed. Waiting for these signs to increase to “sleepy, fighting sleep” or “frequent” sleepiness symptoms poses a heightened risk of serious injury or fatality to the driver and other road users due to drowsiness, and should be avoided.
Supplementary Material
Supplementary material is available at SLEEP online.
Funding
This study was supported by a grant from the Institute of Breathing and Sleep Research (to M.E.H.); by Liberty Mutual Insurance; National Institutes of Health Award 5T32HL7901-14 (to M.L.L.); National Space Biomedical Research Institute Award PF03002 (to M.L.L.); Department of Homeland Security Federal Emergency Management Agency Assistance to Firefighter Grant EMW-2010-FP-00521 (to C.A.C.); National Heart, Lung, and Blood Institute Cooperative Agreement U01-HL111478 (to C.A.C.); National Institute of Occupational Safety and Health Grant R01-OH0103001 (to C.A.C.); National Institute on Aging Grant R01-AG044416 (to C.A.C.); and an endowed professorship provided to Harvard Medical School by Cephalon, Inc. (to C.A.C.). The content of this article is solely the responsibility of the authors and does not necessarily represent the official views of the Federal Emergency Management Agency, Assistance to Firefighters Grant Program, National Institutes of Health, National Space Biomedical Research Institute, Institute of Breathing and Sleep, or Liberty Mutual Insurance Company. The federal sponsors did not have a role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, or approval of the manuscript.
Acknowledgments
We thank the participants for taking part in the study. The authors acknowledge the contributions of Joseph Ronda for his technical expertise, Dr. Murray Johns for his advice concerning ocular parameters, Mr Michael Shreeve for research assistance and Mr Michael Lee for overseeing the conduct of the study.
Disclosure Statement
Financial disclosure: The authors report no conflicts of interest related to the results reported in this paper. In the interest of full financial disclosure, they report: CA has received a research award/prize from Sanofi-Aventis; contract research support from VicRoads, Transport Accident Commission, Rio Tinto Coal Australia, National Transport Commission, Tontine/Pacific Brands, and the Australian Automobile Association; industry funding through ARC Linkage scheme with Seeing Machines and Cogstate Ltd; lecturing fees from Brown Medical School/Rhode Island Hospital, Ausmed, Healthmed and TEVA Pharmaceuticals; and reimbursements for conference travel expenses from Philips Healthcare. In addition, she has served as a consultant to the Rail, Bus, and Tram Union, the Transport Accident Commission (TAC), the National Transportation Committee (NTC), VicRoads, and Melius Consulting. CAC reports grants and contracts to BWH from Dayzz Live Well, Delta Airlines, Jazz Pharma, Puget Sound Pilots, Regeneron Pharmaceuticals/Sanofi; is/was paid consultant/speaker for Inselspital Bern, Institute of Digital Media and Child Development, Klarman Family Foundation, M. Davis and Co, National Council for Mental Well-being, National Sleep Foundation, Physician’s Seal, SRS Foundation, State of Washington Board of Pilotage Commissioners, Tencent, Teva Pharma Australia, With Deep and Vanda Pharmaceuticals, in which CAC holds an equity interest; received travel support from Aspen Brain Institute, Bloomage International Investment Group, Inc., Dr. Stanley Ho Medical Development Foundation, German National Academy of Sciences, Ludwig-Maximilians-Universität München, National Highway Transportation Safety Administration, National Safety Council, National Sleep Foundation, Salk Institute for Biological Studies/Fondation Ipsen, Society for Research on Biological Rhythms, Stanford Medical School Alumni Association, Tencent Holdings, Ltd, and Vanda Pharmaceuticals; receives research/ education gifts through BWH from Arbor Pharmaceuticals, Avadel Pharmaceuticals, Bryte, Alexandra Drane, Cephalon, DR Capital Ltd, Eisai, Harmony Biosciences, Jazz Pharmaceuticals, Johnson & Johnson, Mary Ann & Stanley Snider via Combined Jewish Philanthropies, NeuroCare, Inc., Optum, Philips Respironics, Regeneron, Regional Home Care, ResMed, Resnick Foundation (The Wonderful Company), San Francisco Bar Pilots, Sanofi SA, Schneider, Simmons, Sleep Cycle AB. Sleep Number, Sysco, Teva Pharmaceuticals, Vanda Pharmaceuticals; receives royalties from the New England Journal of Medicine; McGraw Hill; Houghton Mifflin Harcourt/Penguin; and Philips Respironics, Inc. for the Actiwatch-2 and Actiwatch-Spectrum devices. MH has received research funding from the Cooperative Research Center for Alertness Safety and Productivity, contract research support from Vicroads, Shell International, and Rio Tinto, and equipment support for research from Optalert and Seeing Machines. He has served as a consultant for Vicroads, the National Transport Commission, Victoria Police, and Bus Safety Victoria and received lecturing fees from TEVA Pharmaceuticals, Biogen, and Astra-Zeneca. Nonfinancial Disclosure: The authors report no conflicts of interest related to the results reported in this paper. In the interest of full nonfinancial disclosure, they report: CA has served as an expert witness and/or consultant about fatigue and drowsy driving, and was a Theme Leader in the Cooperative Research Center for Alertness, Safety, and Productivity. CAC is/was an expert witness in legal cases, including those involving Advanced Power Technologies, Aegis Chemical Solutions, Amtrak; Casper Sleep Inc, C&J Energy Services, Catapult Energy Services Group, Covenant Testing Technologies, Crete Carrier Corporation, Dallas Police Association, Enterprise Rent-A-Car, Espinal Trucking/ Eagle Transport Group/Steel Warehouse Inc, FedEx, Greyhound, Pomerado Hospital/Palomar Health District, PAR Electrical Contractors, Product & Logistics Services LLC/Schlumberger Technology, Puckett EMS, Puget Sound Pilots, Top Run Energy Services Union Pacific Railroad, UPS, and Vanda Pharmaceuticals; CAC also serves as the incumbent of an endowed professorship given to Harvard by Cephalon. CAC’s interests were reviewed and managed by Brigham and Women’s Hospital and Mass General Brigham by their conflict of interest policies.
Author Contributions
All authors have made substantial contributions to the work presented and have approved the final version of the manuscript. CA, WH, CAC, and MH designed the study with input from YL and COB. CA, AC, CAC, and MH developed the research questions, and M.L.L., WH, YL, COB, and MH were responsible for the collection of data. CA and AC analyzed and interpreted the data. CA wrote the manuscript with edits and approvals from all authors.
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