Cellular telephones may be a convenient tool for drivers, but a new study indicates they may quadruple crash risk when they're in use.

Published in the New England Journal of Medicine, the study looked at 699 Canadian drivers who had cellular telephones and were involved in motor vehicle crashes resulting in substantial property damage but no personal injury.

University of Toronto researchers Donald A. Redelmeier and Robert J. Tibshirani compared each driver's phone use immediately preceding the collision to the same time periods on several days before the crash day. Phone billing records were used to analyze call patterns. Overall, 170 drivers had used a cellular phone within 10 minutes before their crashes.

Redelmeier and Tibshirani found the risk of collision when using a cellular telephone was four times higher than the risk when a cellular phone wasn't being used. After accounting for such driver characteristics as age and driving experience, the relative crash risk still was elevated.

The researchers caution the study "data do not indicate the drivers were at fault in the collisions; it may be that cellular telephones merely decrease a driver's ability to avoid a collision caused by someone else."

An unexpected finding is that the use of hands-free cellular telephones appeared to make no difference in crash risk compared with drivers who used hand-held phones. One possible reason is that "motor vehicle collisions result from a driver's limitations with regard to attention rather than dexterity," study authors explain.

Elisa R. Braver of the Institute points out, "This finding is inconclusive because only 148 study participants had hands-free cellular telephones."

Sales of cell phones in 1995 in the United States exceeded the country's birth rate, study authors noted.