Driver understanding of the current U.S. system of yellowwhite pavement markings was assessed through a driver survey. The survey was used to evaluate drivers ability to describe the pavement marking color code, drivers reliance on pavement marking patterns when interpreting marking messages, and drivers reliance on pavement marking color when interpreting marking messages. Researchers surveyed 851 drivers in 5 states, with respondents representing 47 states, the District of Columbia, and Puerto Rico. The survey results indicate that drivers tend to use signs and other traffic as the primary cue to determine whether a road is one-way or two-way. A substantial proportion of respondents had an understanding of the use of marking color to differentiate between one-way and two-way roads, but this knowledge is not the primary tool that drivers use to distinguish the direction of travel on a road. Approximately 75% of the drivers surveyed understood the basic concept that a single broken yellow line separates opposing traffic on a two-lane road. The presence of a solid line (either double solid or solid and broken) in the centerline increases comprehension of directional flow to approximately 85%; more than 90% of the drivers surveyed understood that a solid line (either double solid or solid and broken) prohibits passing. Almost 95% of drivers indicated that passing is permitted with a broken line. The survey results indicate that the yellowwhite pavement marking system is better understood than previously believed.