"We are convinced that legislation forbidding the use of hand-held cellphones. . . . will not be effective," the letter said. Such laws "may erroneously imply that hands-free phones are safe to use while driving."
The letter was based on a lengthy review of worldwide research on driver distraction conducted at the National Highway Traffic Safety Administration, a branch of the Department of Transportation. In that 2003 review, the agency's researchers for the first time estimated fatalities linked to cellphone use by drivers, putting the toll at 955 deaths in 2002. They predicted that it would only rise because of the growing use of cellphones and especially such activities as text messaging, former agency officials said.
After a June, 2003 meeting with Department of Transportation authorities, the letter was drafted but then spiked. The fatality estimate was never made public.
"They don't put the numbers out there because the numbers make it a lot harder to explain why you haven't been more active," said Bill Walsh, former senior associate administrator of the agency.
An agency spokesman, Rae Tyson, declined to comment.
Other published research, however, has resulted in similar findings. A 2003 study by the Harvard Center for Risk Analysis estimated that there are about 2,600 deaths and 12,000 serious to critical injuries a year in crashes involving drivers using cellphones.
Two widely cited studies found a fourfold greater crash risk for drivers using cellphones than for normal driving -- with nearly identical risks for hand-held and hands-free phones. The studies looked at drivers and collisions in Canada and Australia, where cellphone records were available for analysis, unlike the U.S.
A 2006 study by David L. Strayer and colleagues at the University of Utah found that drivers tested on simulators performed about the same when they used cellphones as when they had a blood alcohol-level of 0.08%, which made them legally drunk. The drivers actually did better in braking and avoiding rear-end collisions when alcohol-impaired than when they were talking on hand-held or hands-free phones.
There are some skeptics. A 2006 paper co-authored by James E. Prieger, a professor of public policy at Pepperdine University in Malibu, found that the link between cellphones and collisions was less conclusive, and the crash risks probably lower, than indicated in some of the most prominent studies.
