Do colored lane markings improve road safety? Causal evidence from Seoul

Colored lane markings are a recent traffic safety intervention in South Korea, designed to improve driver awareness and visual guidance. This study aims to evaluate their effectiveness in reducing traffic crashes. Specifically, 82 road segments in Seoul where the markings were installed were analyzed by comparing crash trends before and after the intervention using data from 2010 to 2024. To estimate the intervention's effect, a counterfactual analysis was conducted by constructing a baseline scenario representing crash trends in the absence of the intervention. The causal impact of the colored markings was then identified by comparing this baseline with observed outcomes. The results show that the implementation of colored lane markings led to an average 26.7 % reduction in crash rates at statistically significant sites. To identify where the intervention was most effective, the relationship between surrounding land use and observed safety outcomes was examined. The analysis indicates that the markings were more effective on highways and arterial roads, which tend to have higher speeds and simpler traffic conditions. In contrast, roads in dense urban areas showed limited improvements. This outcome is attributable to complex traffic conditions and high levels of visual and environmental clutter. Taken together, these findings suggest that the intervention is highly effective and provides safety benefits on arterial networks.