How does sleep or lack of it factor in transportation accidents? And what's the solution to the problem? We spoke with Charles Czeisler, a professor of sleep medicine at Harvard Medical School.

These attentional failures are common in our sleep-deprived society. In fact, there are two million people who admit to falling asleep at the wheel. One out of five motor vehicle accidents are related to sleep deprivation, which adds up to a million crashes a year and 7,500 deaths. That doesn't count train or plane crashes, of course.

I'd want to know when he started his shift. The train began its journey at 5:54 a.m. The accident happened at 7:20 a.m. If you stay up all night or get up