U.S. workers squeeze more hours into their workday and still find time to play by cutting back on sleep, a new study found.

Mathias Basner, a researcher at the University of Pennsylvania School of Medicine, studied 47,731 adults and found that time spent at work is the single biggest determinant of how much sleep they get on a typical day, USA Today said Thursday.

The study, published in the journal Sleep, said traffic and commuting time came in second.

The National Sleep Foundation estimates that sleep-deprived drivers cause more than 100,000 automobile crashes a year, the newspaper said.

The study said people who cut back on sleep during the week try to catch up on the weekend, although sleep experts suggest people who continually cut back on sleep might never catch up.

Copyright 2007 by United Press International