Societal risk reduction in road network design: Outcome assessment on a controlled benchmark network

This paper introduces a framework for the road network design problem in which societal risk is adopted as the objective function. The consolidated approach for network design problem considers the minimizing total travel time or the maximization of user utilities; in this paper the societal risk is adopted, and the results are compared with consolidated approach. The model is formulated for congested road networks under stationary conditions and for endogenous flow events (e.g. road accident), explicitly accounting for behavioural constraints, technical limitations, and regulatory requirements. The proposed methodology is assessed on a controlled benchmark network, enabling reproducible and interpretable analyses while ensuring rigorous evaluation of the individual effects of the investigated parameters, which are often difficult to isolate in applications in real size systems. The analyses investigate the interaction between flow constraints, travel time, and risk, showing how alternative network design solutions can effectively reduce societal risk while preserving acceptable system performance. The results obtained minimizing societal risk and travel time are compared for compare the proposed approach and the consolidated one. The results highlight the policy relevance of incorporating risk reduction as a primary objective in transport planning and open the way to future research directions, including extensions to more realistic and large-size transport systems.