Quantifying risk and accident severity on staged-development expressways: An Ordered Logit approach
With limited public investment, phased investment strategies (2-lane or limited 4-lane configurations) are widely adopted in Vietnam. However, this model poses safety risks due to the lack of median barriers and continuous emergency lanes. This study analyzes and quantifies factors influencing traffic accident severity using 170 accident records from 2018-2025. Integrating descriptive statistics and hierarchical logistic regression, the research identifies heavy trucks as the primary vehicles in over 71% of collisions. The model reveals that accidents on weekdays pose a severity risk 2.445 times higher than on weekends. Notably, "vehicle overturn or run-off-road" accidents - a direct result of inadequate emergency lanes - increase the probability of severe outcomes by 4.178 times. These findings provide a scientific basis for prioritizing infrastructure upgrades and optimizing traffic management on phased expressways.