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Driver sleepiness and risk of serious injury to car occupants: population based case control study

BMJ 2002; 324 doi: (Published 11 May 2002) Cite this as: BMJ 2002;324:1125
  1. Jennie Connor, senior lecturer in epidemiology (j.connor{at},
  2. Robyn Norton, professor of public healthb,
  3. Shanthi Ameratunga, senior lecturer in epidemiologya,
  4. Elizabeth Robinson, biostatisticiana,
  5. Ian Civil, director of trauma servicesc,
  6. Roger Dunn, associate professord,
  7. John Bailey, scientiste,
  8. Rod Jackson, professor of epidemiologya
  1. a Division of Community Health, University of Auckland, Private Bag 92019, Auckland, New Zealand
  2. b Institute for International Health, University of Sydney, Newtown, New South Wales 2042, Australia
  3. c Department of Surgery, Auckland Hospital, Private Bag 92024, Auckland, New Zealand
  4. d Department of Civil and Environmental Engineering, University of Auckland
  5. e Bailey Partnership, Porirua 6006, New Zealand
  1. Correspondence to: J Connor
  • Accepted 29 January 2002


Objectives: To estimate the contribution of driver sleepiness to the causes of car crash injuries.

Design: Population based case control study.

Setting: Auckland region of New Zealand, April 1998 to July 1999.

Participants: 571 car drivers involved in crashes where at least one occupant was admitted to hospital or killed (“injury crash”); 588 car drivers recruited while driving on public roads (controls), representative of all time spent driving in the study region during the study period.

Main outcome measures: Relative risk for injury crash associated with driver characteristics related to sleep, and the population attributable risk for driver sleepiness.

Results: There was a strong association between measures of acute sleepiness and the risk of an injury crash. After adjustment for major confounders significantly increased risk was associated with drivers who identified themselves as sleepy (Stanford sleepiness score 4-7 v 1-3; odds ratio 8.2, 95% confidence interval 3.4 to 19.7); with drivers who reported five hours or less of sleep in the previous 24 hours compared with more than five hours (2.7, 1.4 to 5.4); and with driving between 2 am and 5 am compared with other times of day (5.6, 1.4 to 22.7). No increase in risk was associated with measures of chronic sleepiness. The population attributable risk for driving with one or more of the acute sleepiness risk factors was 19% (15% to 25%).

Conclusions: Acute sleepiness in car drivers significantly increases the risk of a crash in which a car occupant is injured or killed. Reductions in road traffic injuries may be achieved if fewer people drive when they are sleepy or have been deprived of sleep or drive between 2 am and 5 am.

What is already known on this topic

What is already known on this topic Driver sleepiness is considered a potentially important risk factor for car crashes and related injuries but the association has not been reliably quantified

Published estimates of the proportion of car crashes attributable to driver sleepiness vary from about 3% to 30%

What this study adds

What this study adds Driving while feeling sleepy, driving after five hours or less of sleep, and driving between 2 am and 5 am were associated with a substantial increase in the risk of a car crash resulting in serious injury or death

Reduction in the prevalence of these three behaviours may reduce the incidence of injury crashes by up to 19%


  • Contributors JC contributed to the study design, coordinated data collection, and was mainly responsible for the statistical analysis and writing the paper and is guarantor. RN and RJ were mainly responsible for the study design and contributed to the interpretation of the data and writing the paper. SA, ER, IC, RD, and JB contributed to the study design and writing of the paper. ER also contributed to the statistical analysis.

  • Funding Health Research Council of New Zealand and Transit New Zealand. JC is supported by the Health Research Council and the Australasian Faculty of Public Health Medicine.

  • Competing interests None declared.

  • Accepted 29 January 2002
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