Medical residents often work shifts of 24 hours or longer; this has led to worries that their sleepiness could endanger patients—and, during the drive home after work, themselves and other drivers. For a new study, researchers asked interns (first-year residents) about car accidents and near misses.

What the researchers wanted to know: How does a work schedule affect driving safety for medical interns?

What they did: Everyone who graduated from med school or was matched to a residency program in 2002 was sent a letter offering money for participation in a Harvard study of work hours and safety. Those who agreed answered monthly questionnaires through May 2003; some participants were also asked to keep daily records of their work hours. Interns reported an average of four extended work shifts a month.

What they found: Interns were more than twice as likely to have an accident if they were driving home after an extended work shift (24 hours or longer) than if they were coming home after a regular shift. They were nearly six times as likely to have a near miss after an extended shift as after a regular shift. Each extended shift worked in a month increased the risk of having a crash that month by 10 percent.

What the study means to you: Letting interns sleep more could reduce car crashes. But this also raises the question of whether interns who are too sleepy to drive carefully are also too tired to take care of patients. After the study ended, rules went into effect by the Accreditation Council for Graduate Medical Education mandating a 30-hour limit on a work shift. There were 275 reports in this study of working more than 40 hours in a row.

Caveats: The interns who volunteered for this study—fewer than 3,500 of the 18,447 who were invited—may not be representative of residents as a whole. But they didn't know what the study was for, exactly, so the researchers think that the interns who responded probably weren't purposefully skewing the results.

Find out more: The Accreditation Council for Graduate Medical Education has the rules on work hours.

Read the article: Barger, L.K. et al. "Extended Work Shifts and the Risk of Motor Vehicle Crashes Among Interns." New England Journal of Medicine. Jan. 13, 2005, Vol. 352, No. 2, pp. 125–134.

Abstract online: http://content.nejm.org