Cell phone use while driving has been estimated to cause 333,000 crashes each year, resulting in 2,600 deaths and $43 billion in societal costs. An increasing number of states have implemented cell phone laws banning hand-held phone use and texting while driving, but it remains unclear whether these laws reduce calling, texting, or crashes among young drivers. The Objective of this application is to determine across multiple states the impact of cell phone laws and their enforcement on calling and texting while driving, and on rates of injurious and fatal traffic crashes among drivers under age 25. Its Central hypothesis is that, the effectiveness of cell phone laws is impacted by certain provisions of the law, and that most laws have little or no impact unless they include a high degree of enforcement. It will pursue the following specific aims: 1) Determine which provisions of hand-held cell phone bans and which level of enforcement actually reduce roadside-observed calling while driving among drivers under age 25; 2) Identify which provisions of texting bans and which level of enforcement reduce self-reported texting or emailing while driving among high school students; and 3) Determine which provisions of hand-held cell phone bans and texting bans, and which level of enforcement reduce traffic crash rates among drivers under age 25. The following legislative provisions will be examined: mode of enforcement (primary enforcement-officers can stop a vehicle for cell phone use only; or secondary enforcement-driver must first be cited for another infraction), total cell phone ban for drivers < age 18 (yes or no), texting ban fr all ages (yes or no), amount of fine ( $100 or < $100), license delay for drivers < 18 ( 6 months, < 6 months, or no), and penalty points on license (yes or no). The level of enforcement will be measured by the number of cell-phone-related citations per driver-year. The data sources include: 2000- 2013 National Occupant Protection Use Survey (roadside-observed cell phone use), 2011 and 2013 national Youth Risk Behavior Surveillance data (self-reported texting or emailing while driving), and 2000-2013 state- based Police Accident Reports (injurious crashes) and Fatality Analysis Reporting System (fatal crashes). Multilevel logistic and negative binomial models will be used to estimate the effects of state-level laws on individual-level cell phone use while driving and state-level crash rates. Guided by strong preliminary data, this study will use several innovative approaches. Its unique multi-state approach differentiates the effects of laws among states due to variations in legislative provisions and the level of enforcement. There are multiple independent measures of impact: roadside-observed cell phone use, self-reported texting while driving, and traffic crash rates. It will be the first study to control for an importnt confounder (increasing cell phone popularity). Given that 42 states and District of Columbia have enacted at least one type of cell phone law, the significance is that, the findings of this study should inform policymakers' efforts to upgrade existing, or develop new laws, and better enforce laws that can effectively reduce cell phone use while driving, and traffic crashes.