OBJECTIVE: Distracted driving contributes to a large proportion of motor vehicle crashes, yet little is known about the prevalence of distracted driving and the specific types of distracting behaviors. The objective of this study was to estimate the prevalence of driver distraction using a roadside observational study design. METHODS: A cross-sectional survey involving direct roadside observation was conducted at 11 selected intersections. Trained investigators observed a sample of passenger vehicles and recorded distraction-related behaviors, driver characteristics, and contextual factors such as vehicle speed and traffic flow. RESULTS: Of the 3,265 drivers observed, the prevalence of distracted driving was 32.7%. Among those involved in a distracting activity, the most frequently observed distractions included interacting with another passenger (53.2%, where passengers were present), talking on the phone (31.4%), external-vehicle distractions (20.4%), and texting/dialing a phone (16.6%). The prevalence of talking on the phone was higher among females than males (38.6% vs. 24.3%), whereas external vehicle distractions were higher among males than females (25.8% vs. 24.3%). Drivers <30 years were observed being engaged in any distracting activity, interacting with other passengers, and texting/dialing more frequently than drivers aged 30-50 and >50 years. Drivers were engaged in distracting behaviors more frequently when the car was stopped. CONCLUSIONS: When using similar methodology, roadside observational studies generate comparable prevalence estimates of driver distraction as naturalistic driving studies. Driver distraction is a common problem among passenger vehicle drivers. Despite the increased awareness on the dangers of texting and cell phone use while driving, these specific activities were 2 of the most frequently observed distractions. There is a continued need for road safety education about the dangers of distracted driving, especially for younger drivers.