This report assesses the risks and benefits associated with cellular phone use while driving. The interest of policymakers in this issue has been heightened by the recent decisions of selected foreign countries and several U.S. localities to restrict or prohibit the use of cellular phones while driving. The weight of the scientific evidence to date suggests that use of a cellular phone while driving does create safety risks for the driver and his/her passengers as well as other road users. The magnitude of these risks is uncertain but appears to be relatively low in probability compared to other risks in daily life. It is not clear whether hands-free cellular phone designs are significantly safer than hand-held designs, since it may be that conversation per se rather than dialing/handling is responsible for most of the attributable risk due to cellular phone use while driving. The benefits of using this communications device while driving appear to be important. They include benefits to the users, households, social networks, businesses, and communities. Many of these benefits, which include public health and safety considerations, have not yet been recognized or quantified. Simple suggestions that drivers can "pull over" on the side of the road to make calls from cellular phones are unrealistic and, in certain situations, potentially dangerous. It is not known which of the benefits of cellular phone use would be foregone under various regulatory scenarios. Cellular phone use while driving should be a concern of motorists and policymakers. We conclude that although there is evidence that using a cellular phone while driving poses risks to both the driver and others, it may be premature to enact substantial restrictions at this time. Indecision about whether cellular phone use while driving should be regulated is reasonable due to the limited knowledge of the relative magnitude of risks and benefits. In light of this uncertainty, government and industry should endeavor to improve the database for the purpose of informing future decisions of motorists and policymakers. In the interim, industry and government should encourage, through vigorous public education programs, more selective and prudent use of cellular phones while driving in order to enhance transport safety.