In a groundbreaking investigation poised to reshape the future of road safety, researchers from Incheon National University in South Korea have unveiled novel insights into how the intricate interplay between road design features and traffic patterns directly and indirectly influences crash risks. With global road fatalities surpassing 1.19 million annually, the urgency for innovative strategies to enhance traffic safety has never been more critical. This pioneering study transcends traditional perspectives by exploring not only the immediate influence of road attributes on crash occurrences but also how these characteristics modulate traffic speed and volume, which in turn affect crash likelihood.
The study, spearheaded by Assistant Professor Wookjae Yang, delves into a 68-kilometer stretch of a national highway in South Korea, employing advanced quantitative techniques such as principal component analysis (PCA) and piecewise structural equation modeling (PSEM). These analytic methods enable a nuanced deconstruction of complex relationships, isolating both direct effects of physical road features and their indirect consequences mediated through dynamic traffic conditions. By leveraging this robust analytical framework, the research addresses a critical gap in road safety literature, where prior inquiries often treated traffic speed and volume as static variables rather than interactive mediators.
Central to the research findings is the categorization of road attributes into three primary components: pedestrian and roadside facilities (PC1), cross-sectional and intersection conditions (PC2), and road surface texture and curvature (PC3). The most profound influence emerged from PC1, encompassing modifiable features such as sidewalks, lighting systems, and pedestrian crossings, which exhibited the strongest direct correlation with reduced crash frequencies, particularly for run-off-road incidents. This insight underscores the vital role of easily alterable roadside infrastructures in upgrading safety outcomes beyond static geometric road designs.
Interestingly, while PC2 and PC3—representing structural elements like intersections, lane widths, and curvature—did not manifest significant direct impacts on crash rates, their indirect effects channeled through alterations in traffic speeds and volumes were notable. This finding nuances existing regulatory standards, suggesting that even seemingly rigid design elements exert influence through their modulation of driver behavior and traffic flow, factors often underappreciated in safety evaluations. The relative uniformity of design standards along the studied highway may have masked direct effects, yet the indirect pathways highlight complex mechanisms at play.
This research carries substantial implications for transportation agencies and policymakers worldwide. By drawing attention to the potent influence of pedestrian and roadside amenities—which can be adjusted during routine maintenance—over fixed geometric features often anchored during initial design stages, the findings advocate for a paradigm shift in road safety management. Emphasizing mutable operational elements allows for more agile, cost-effective interventions, facilitating iterative improvements without the prohibitive expenses of wholesale infrastructure redesign.
Furthermore, the study critiques global road safety assessment protocols such as the International Road Assessment Programme (iRAP) for their tendency to conflate static geometric features with dynamic operational factors. The researchers recommend a refined analytical approach that explicitly distinguishes these dimensions, thereby enabling targeted investments and strategic prioritization. Such refinement could unlock unprecedented precision in predicting and mitigating crash risks, ultimately saving lives and reducing the societal burden of traffic accidents.
From a methodological viewpoint, the application of piecewise structural equation modeling marks a significant advancement in transportation safety research. Unlike conventional regression analyses that often overlook the mediating variables, PSEM facilitates a holistic examination of causal chains, accounting for multifaceted interactions that govern real-world phenomena. This holistic approach reveals the cascading effects of road design modifications, providing empirical foundations for integrated safety interventions encompassing infrastructure, traffic management, and behavioral considerations.
The implications of traffic speed and volume functioning as mediators also challenge the conventional wisdom that regards these metrics solely as control variables. Instead, the study positions them as dynamic intermediaries shaped by the physical environment, which, in turn, shape crash likelihood. This reconceptualization encourages a multifactorial perspective on safety that integrates physical, behavioral, and systemic factors, aligning with contemporary understandings of complex urban systems.
Assistant Professor Yang emphasizes that interventions focused on enhancing pedestrian and roadside facilities not only reduce direct crash occurrences but also foster safer driving behaviors by moderating speed. Well-lit sidewalks, clearly marked pedestrian crossings, and protective roadside barriers serve dual functions: they safeguard vulnerable road users and signal to drivers the need for cautious navigation, thereby attenuating speed-related risks. This dual mechanism attests to the importance of comprehensive design strategies that harmonize infrastructure and human factors.
Moreover, the research accentuates the operational flexibility advantage, whereby pedestrian and roadside elements can be upgraded through regular maintenance cycles without necessitating major reconstruction. This insight opens avenues for more responsive safety policies, wherein targeted adjustments respond swiftly to emerging risk profiles identified through ongoing monitoring and data analytics. Such adaptability is crucial in fast-evolving urban environments facing demographic shifts, traffic growth, and technological disruption.
This study’s relevance extends beyond South Korea’s national highways, offering valuable lessons for global road safety endeavors. Particularly in rapidly urbanizing regions where infrastructure must balance efficiency and safety under constrained resources, prioritizing modifiable roadside features can yield tangible safety dividends. Integrating these findings into international standards and local policies could catalyze more sustainable, context-sensitive safety frameworks globally.
In sum, this landmark study by Dr. Wookjae Yang and his team illuminates the critical dynamics underpinning road safety, unveiling both direct and indirect pathways through which road environments shape crash risk. Bridging gaps between physical infrastructure and traffic behavior, it pioneers an integrative analytical lens that promotes smarter, safer road systems. As cities and nations strive to meet ambitious goals like halving road traffic deaths by 2030, incorporating such nuanced evidence into practice will be indispensable. This research not only charts a path toward more effective collision prevention but also underscores the broader imperative of harmonizing design, operation, and policy in the pursuit of safer mobility for all.
Subject of Research:
Road design elements and traffic condition interactions affecting crash likelihood and types on national highways.
Article Title:
Direct and indirect effects of road attributes on traffic safety
News Publication Date:
July 1, 2025
Web References:
https://doi.org/10.1016/j.jsr.2025.02.017
References:
Yang, W., & Han, S. (2025). Direct and indirect effects of road attributes on traffic safety. Journal of Safety Research, 93. https://doi.org/10.1016/j.jsr.2025.02.017
Image Credits:
Dr. Wookjae Yang from Incheon National University (INU), South Korea
Keywords:
Urban planning, Urban studies, Traffic safety, Road design, Pedestrian facilities, Traffic speed and volume, Transportation engineering, Roadside infrastructure, Crash risk analysis
