A recent study by the Texas A&M Transportation Institute provides the most compelling evidence yet that wider paint lines on roadway shoulders (commonly called edge lines) are a cost-effective, statistically sound approach to reducing crashes and fatalities on rural two-lane highways. The study, entitled “An Evaluation of the Effectiveness of Wider Edge Line Pavement Markings,” was sponsored by the American Glass Bead
“This is the first formal evidence of a correlation between wider edge lines and improved crash safety,” said Paul Carlson, a TTI Research Engineer and one of the authors of the study. “Previous studies over the last 10 years were small and naïve in analyses, and lacked data to provide statistically significant results.”
In the past, many states adopted wider edge lines (6 inches instead of 4 inches) for a range of reasons, but adoption has been slow and uncoordinated without sound empirical findingsto support the decision, according to the study. Glass bead products are frequently used for highway safety markings such as these, providing the light-reflective lane markings found on highways around the world. Previous studies found indirect evidence to support wider edge lines, but evidence showing direct reduction in crashes was difficult to provide due to data issues. The recent analysis of Federal Highway Administration data from three states (Kansas, Michigan and Illinois) provides the necessary evidence to support adoption of wider edge lines (see Safety effects of wider edge lines on rural, two-lane highways).
“With the ultimate goal being highway safety, transportation agencies across the United States now have strong data to support the undertaking of a relatively low-cost measure to improve highway safety and reduce fatalities,” said Kevin Goforth, president of the American Glass Bead Manufacturers’
The study demonstrated that wider edge lines have been shown to reduce total crashes 15 to 30 percent and fatal-plus-injury crashes 15 to 38 percent. In addition, the benefit-cost ratio for wider edge lines is $33 to $55 for each $1 spent, which is similar to shoulder rumble strips. If an agency is considering installing rumble strips as a safety countermeasure but is concerned about potential noise or pushback from the bicycle community, wider edge lines appear to offer similar results but without the concerns.
Since the safety benefits of wider edge lines are now better documented, the study suggests that it would be beneficial if the Manual on Uniform Traffic Control Devices was amended so that minimum edge-line width on rural two-lane highways was 6 inches. Agencies would then be able to implement the policy in a uniform and consistent manner .