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Medical Interns’ Risk for Car Crashes Linked With Extended Shifts in NIOSH-Funded Study

January 13, 2005
NIOSH Update:

Contact: Fred Blosser (202) 401-3749

First-year doctors in training, or medical interns, who work shifts of longer than 24 hours are more than twice as likely to have a car crash leaving the hospital and five times as likely to have a “near miss” incident on the road as medical interns who work shorter shifts, according to a study co-funded by the National Institute for Occupational Safety and Health (NIOSH) that was reported in the January 13 issue of the New England Journal of Medicine.

The article, “Extended Work Shifts and the Risk of Motor Vehicle Crashes among Interns,” is the third in a series of studies on the impact of extended work hours and fatigue on interns conducted by the Divisions of Sleep Medicine at the Brigham and Women’s Hospital and the Harvard Medical School in Boston. The first two studies were published in the October 28, 2004, issue of NEJM. All three were co-funded by NIOSH and the Agency for Healthcare Research and Quality in the U.S. Department of Health and Human Services.

Laura K. Barger, Ph.D., Research Associate in Medicine at the Brigham and Women’s Hospital and Harvard Medical School, and her colleagues recruited 2,737 interns from medical institutions around the country to fill out detailed monthly surveys recording their work hours, frequency of shifts of more than 24 hours and driving safety records, including car accidents, near-miss incidents in which property damage was narrowly avoided and incidents involving their falling asleep while driving or while stopped in traffic. More than 17,000 surveys were collected between April 2002 and May 2003. Researchers also randomly selected 7 percent of study participants to keep daily work diaries that were verified through direct observation.

The study found that the majority of interns routinely worked more than 30 consecutive hours, and they reported that they were awake 96 percent of their time in the hospital on average. Also, during the 12-month study period, interns reported working an average of 80 hours or more during 46 percent of work weeks and 100 hours or more per week during 11 percent of work weeks.

“This study clearly shows that the impact of overly long work hours and fatigue extend outside the hospital,” said Carolyn M. Clancy, M.D., AHRQ’s director. “These studies have provided a foundation of evidence for ensuring that work shifts in hospitals are adequate to provide the best training for young physicians without posing a danger to their own health and safety as well as that of their patients and others.”

“NIOSH is working closely with diverse partners to address the implications of long working hours and non-traditional work schedules for job-related health and safety,” said NIOSH Director John Howard, M.D. “These new findings are a valuable addition to the data needed by researchers to help employers and employees maximize health, safety, and productivity in designing work schedules.”

Study participants reported a total of 320 accidents during the 12-month study period, including 133 that resulted in treatment in the emergency room, property damage of more than $1,000 or the filing of a police report. Slightly more than 40 percent of the 320 crashes occurred on the commute from work. Every extended shift that was scheduled per month increased the monthly rate of accidents on the commute from work by 16 percent and the monthly rate of any car accident by 9 percent. Interns also were more than twice as likely to fall asleep while driving or more than three times as likely to fall asleep while stopped in traffic in months in which they worked five or more extended shifts.

“Because nearly 70 percent of medical interns who participated in the study commute to work by car, eliminating extended work shifts could prevent a substantial number of accidents,” said Dr. Barger.

Senior author Charles A. Czeisler, Ph.D., M.D., who leads the Harvard Work Hours, Health, and Safety Group, the team that conducted all three studies, and who is Baldino Professor of Sleep Medicine and Director of the Division of Sleep Medicine at Harvard Medical School, said, “It is unsafe to get behind the wheel of a car after working for 24 consecutive hours. The health care profession has a duty to protect its young trainees from exposure to the well-known hazard of drowsy driving, which causes over 100,000 motor vehicle crashes on our nation’s highways every year.”

The new study is available on line at More details about the previously published studies funded by NIOSH and AHRQ are available at

Recent NIOSH findings from the scientific literature on the relationship between long working hours and employee health and safety are available at NIOSH’s findings and recommendations on administering or coping with shiftwork to reduce health and safety concerns are available at

For more information about NIOSH research, call the NIOSH toll-free number, 1-800-35-NIOSH (1-800-356-4674) or visit the NIOSH web page,