Direct and indirect effects of road attributes on traffic safety

Providing safe road infrastructure is increasingly gaining attention worldwide as part of the effort to reduce road deaths and injuries. Halving road fatalities by 2030 is one of the targets among the Sustainable Development Goals of the United Nations. This study aims to understand how road traffic conditions, including vehicle speeds and volumes, mediate the relationship between road design and traffic safety.

In particular, the study relies on 78 road attributes pertaining to road design features, as published in the International Road Assessment Programme's (iRAP) Star Rating and Investment Plan Manual. The star rating was conducted along a 68 km segment of a national highway in Korea, and these coded data were associated with both traffic and crash data. The traffic data, in this case, the average vehicle volume and speed, are sourced from the View-T platform in Korea. Crash data were obtained from Traffic Accident Analysis Systems in Korea.

The application of principal component analysis (PCA) identified three principal components-principal component (PC) 1 represents attributes related to pedestrians and roadside facilities, PC2 represents cross-sections and intersections, and PC3 represents attributes related to road surfaces and curvatures. In addition, piecewise structural equation modeling confirmed that PC1 is the only component that has a direct effect on the number of crashes.

The finding suggests that pedestrian and roadside facilities easily added or removed during road operations are more critical than geometric attributes established at the road design stage. The study also confirms the indirect effects of the aspects of speed and volume on the likelihood of a crash.