Cellular telephone use has increased significantly in the United States as 97% of residents now own some type of cell phone. The ubiquity of cell phones has introduced concerns with respect to traffic safety as cell phone-related distractions have been shown to affect driving ability and increase crash risk. Various countermeasures have been implemented to address this issue, including public outreach campaigns and targeted enforcement activities. However, the efficacy of such strategies has been the subject of limited research. This paper examines cell phone use rates in consideration of enforcement activities in conjunction with targeted safety messages on roadside dynamic message signs. Two phases of enforcement were conducted in two urbanized areas of Michigan. Data were collected before, during, and after the enforcement period. A two-way random effects logistic regression model was estimated, and the results showed that cell phone use rates were lower during and, particularly, after the enforcement activities were conducted. Use rates were also found to vary based on age, gender, and race, allowing for the identification of target groups for public awareness and outreach campaigns. Use rates were also lower at freeway exit ramps as compared to signalized and stop-controlled surface street intersections. Lastly, cell phone-specific safety messages were associated with lower use rates compared with other message types, suggesting a potential synergistic effect.
