Night shift workers have many more motor vehicle crashes than day workers, particularly during the commute home.
Researchers at Brigham and Women’s Hospital (BWH) and the Liberty Mutual Research Institute for Safety recently found that 37.5 percent of drivers participating in a test drive after working the night shift were involved in a near-crash event. The same drivers, with normal sleep the night before the test, had zero near-crashes.
“Drowsy driving is a major, and preventable, public health hazard,” says Charles A. Czeisler, PhD, MD, FRCP, Chief of the Division of Sleep and Circadian Disorders at BWH, and corresponding author of the study. “These findings help to explain why night shift workers have so many more motor vehicle crashes than day workers, particularly during the commute home. Night shift workers should be advised of the hazards of drowsy driving and seek alternate forms of transportation after night shift work.”
The drowsy driving results were derived from a study of 16 night shift workers who completed a pair of two-hour driving sessions on a closed driving track at the Liberty Mutual Research Institute for Safety. Prior to one of the sessions, participants slept an average of 7.6 hours the previous night, with no night shift work. Prior to the other session, the same participants were tested after working a night shift. The post-sleep and post-night shift drives occurred at approximately the same time of day for each participant.
Physiological measures of drowsiness were collected, including brief micro-sleep episodes, as measured by an EEG, and partial eyelid closure with slow eye movements, which are indicative of the transition from wakefulness to sleep. Driving performance was evaluated by measuring near-crash events, drives terminated due to failure to maintain control of the vehicle, and how often drivers weaved in and out of the lane. Near-crash events were defined as instances where the in-vehicle safety observer applied the secondary brake pedal because the vehicle began to leave the roadway and the driver did not make a corrective maneuver.
“Even veteran night shift workers were vulnerable to the risks associated with drowsy driving, and exhibited reactions similar to behaviors observed in drivers with elevated blood alcohol concentrations,” says Michael L. Lee, PhD, lead author of the study and research fellow in the Division of Sleep and Circadian Disorders at BWH. “A short commute for these drivers is shown to be potentially dangerous and the longer the drive, the greater the risk. Education about drowsy driving and its potential hazards could minimize this risk by prompting shift workers to eliminate or reduce the need to drive after night shift work, and to stop driving when their performance is impaired by drowsiness.”
Each year, nearly half a million crashes and 6,500 fatalities directly result from driver fatigue. The researchers’ work was published in the Proceedings of the National Academy of Sciences.
– Elaine S.