A recent survey by the National Highway Traffic Safety Administration indicates at any given time, about 3 percent of passenger-vehicle drivers are talking on hand-held cell phones.

The agency estimated that 500,000 drivers of passenger vehicles are talking on hand-held cell phones at any given daytime moment throughout the week. The research didn't include those who use hands-free equipment.

The report, which was based on an observational survey of drivers conducted in 50 geographic areas, found the highest use rate observed during the survey (8 percent) was by drivers of vans and SUVs during non-rush hours. The lowest rate was for pickup drivers.

Cell phone use rates by drivers of all passenger vehicles were almost twice as high during non-rush hours as during rush hours. Use rates were higher on weekdays than weekends.

Although the research does not attempt to assess the contribution of cell phone use to traffic crashes, NHTSA estimates that some form of driver distraction - including talking, eating, reading and changing the radio - is a contributing factor in 20 to 30 percent of all crashes.

New York recently became the first state to pass a ban on using cell phones while driving and at least 39 other states also are considering banning the use of cell phones. About 20 foreign countries have established bans.