WASHINGTON: Night shift workers may be at an increased risk for drowsy driving crashes because of disruption to their sleep-wake cycles and insufficient sleep, a new study has warned.New research from Brigham and Women's Hospital (BWH) in US evaluated the daytime driving performance of night shift workers after a night of shift work compared to driving after a night of sleep, and found that 37.5 per cent of drivers participating in a test drive after working the night shift were involved in a near-crash event.The same drivers, with sufficient sleep the night before the test, had zero near-crashes, researchers said.These results demonstrate, for the first time, an increased risk of drowsy driving related motor vehicle crashes, as well as an increase in self-reported and biological measures of drowsiness when operating a real motor vehicle during the daytime following night shift work."Drowsy driving is a major - and preventable - public health hazard," said Charles A Czeisler, chief of the Division of Sleep and Circadian Disorders at BWH."These findings help to explain why night shift workers have so many more motor vehicle crashes than day workers, particularly during the commute home," said Czeisler, corresponding author of the study.In the study, 16 night shift workers completed a pair of 2-hour driving sessions on a closed driving track.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.Researchers found that during the post-night shift drive participants showed increased driver drowsiness, deteriorating driving performance and increased risk of near-crashes.Over one third of the post night-shift drives required emergency braking manoeuvres, while almost half of the drives were terminated early because the participants failed to maintain control of the vehicle.Sleep-related impairment was evident within the first 15 minutes of driving. Participants had a significantly higher rate of lane excursions.Participants had longer blink duration and increased number of slow eye movements. They showed increased drowsiness, impairment and crash risk over the duration of the drive."Even veteran night shift workers were vulnerable to the risks associated with drowsy driving, and exhibited reactions similar to behaviours observed in drivers with elevated blood alcohol concentrations," said Michael L Lee, lead author, 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," said Lee.The study was published in the journal PNAS.