Evaluating the Traffic Functionality of Emergency Transportation Networks: Development of Reachability Indicators and a Decision-Support Tool for Tokyo

Abstract

Ensuring the continuity of emergency transportation networks is essential for effective post-disaster response and recovery. This study develops a quantitative and policy-oriented evaluation framework to assess the traffic functionality of Tokyo’s designated emergency transportation roads by integrating roadside building vulnerability data with seismic retrofit information. Two novel indicators—the Section Reachability Ratio and the Comprehensive Reachability Ratio—are introduced to quantify network accessibility under probabilistic road blockages caused by building collapse. Using Monte Carlo simulation, the framework estimates accessibility probabilities by coupling building-specific seismic performance data with the urban transportation network structure. The results reveal pronounced spatial heterogeneity in retrofit effects and identify segments where improvements in building seismic performance produce measurable gains in network robustness. A structural transition in reachability behavior is observed as accessibility requirements become more stringent, supporting the adoption of a robustness-oriented threshold definition. The study further presents a GIS-integrated evaluation application that operationalizes the proposed indicators within a real-world planning context. Rather than prescribing optimal retrofit decisions, the framework provides a transparent and empirically grounded basis for comparing alternative retrofit scenarios, thereby supporting evidence-based disaster mitigation planning and future optimization-oriented extensions.