Document Type


Publication Date



Sustainable urban development -- Arizona -- Tucson, Floods -- Arizona -- Risk assessment, Transportation -- Reliability, Transportation -- Planning


A flood vulnerability assessment of the City of Tucson, Arizona’s transportation systems was conducted with special reference to low-income and minority neighborhoods. Short-term flooding from extreme storm events pose a serious challenge to transportation system reliability and emergency response in cities across the United States. This problem, which is anticipated to grow over the next century due to climate change, is often hardest on vulnerable populations, including low-income and minority neighborhoods. Our work aimed to advance national research methods for assessing multi-modal transportation degradation due to flooding. We identified priority locations for Tucson to make transportation improvement investments for the purpose of mitigating urban transportation system flooding. This included increasing equitable accessibility to the multi-modal transportation network across three modes: vehicular, bicycle, and public transportation via pedestrian access to bus stops. As a case study, our proposal has national flood hazard transportation vulnerability and equity implications. The project had three stages. In Stage 1 we estimated flood conditions based on a 5-year, 1-hour storm event with FLO-2D and a digital elevation model (DEM) constructed using LiDAR data. In Stage 2 we analyzed neighborhood transportation vulnerability based on overall transportation system performance and use across the three transportation networks. In Stage 3, we performed thirty (the top ten sites for the three modes of transportation) green infrastructure (GI) scenario analyses to determine the impact that GI implementations could have on the multimodal system. Of the thirty areas studied, 93% were part of census tracts with median household incomes below the Tucson average. We found that GI implementation performs most effectively to increase multi-modal access when implemented in moderate flooding conditions. In extreme cases, comprehensive, neighborhood-scale GI implementation did not result in creating greater accessibility during flood events. Rather than municipalities selecting areas for GI implementation that have the highest volumes of flooding or citizen complaints, GI implementation funds may be invested in moderate flooded area for greatest improvement of multimodal access. Future research will assess impact across time durations (rather than simple peak event calculations) and work to optimize GI implementation across multiple benefits for multiple modes of transportation (rather than individual modes). We plan to communicate our findings broadly. This research is a proof of concept for a larger, long-term project to advance national research methods to reduce the impact of chronic flooding on the multi-modal transportation network. Additional funding from NITC and other sources is currently being targeted.


This is a final report, NITC-SS-1262, from the NITC program of TREC at Portland State University, and can be found online at:

The Project Brief associated with this research can be found at:



Persistent Identifier