Assessment of Transportation System Vulnerabilities to Tidal Flooding in Honolulu,Hawaii

Tidal flooding, a tangible, present-day result of sea-level rise, has caused roadway damage and transportation system closures as well as delays, disruptions, and economic losses. There is a need for more research, understanding, and planning for the management of this threat to transportation services. Using data on tidal flooding, transportation networks, land use, and population characteristics, the vulnerability of transportation systems to tidal flooding is assessed for Honolulu, Hawaii. Accessibility measures coupled with population characteristics provide quantitative estimates of travelers’ underlying exposures and vulnerabilities to disruptions. Using GIS and overlay mapping techniques, at-risk roadway segments are identified and Traffic Analysis Zones (TAZs) are ranked in relation to accessibility changes. Trips to work and school, grocery shopping, recreational activities, and emergency services are analyzed. In addition to identifying critical, at-risk facilities, the analysis includes the consideration of vulnerable populations, such as the elderly, young people, those on low incomes, and those with limited transportation options. Using a nonparametric, mean-shift clustering method, TAZs are ranked and prioritized for potential mitigation actions. While 90% of TAZs suffered minimal effects, several experienced up to 100% accessibility reduction. High priority areas are located in Laie, Punalua, Kailua, Waimanalo, Hawaii Kai, and near Honolulu Harbor. The analysis is useful, not just for transportation system planners but also for first responders, emergency managers, and others working to increase transportation system resilience. Designed as a flexible planning and decision-support tool, the approach could be adapted to plan for other types of hazards such as tsunamis or storm surges as well.