Understanding Flood Risk in Public Transit Systems: Insights from Accessibility and Vulnerability Analysis in Iowa

Flooding is a major challenge for urban transportation systems, hindering access to essential services and jobs, especially for vulnerable populations. This study examines the impact of large flood extents on public transportation in Johnson and Linn counties, Iowa, United States, focusing on flood-prone bus routes, reduced service frequency, and access to job locations. Using Geographic Information System (GIS) tools, flood maps were integrated with General Transit Feed Specification (GTFS) data, while a demographic analysis highlighted the social vulnerability of the impacted communities. The findings reveal that transit disruptions during flooding are significant, with service losses totaling 526 visits during AM peak hours in Johnson County under a 500-year flood scenario. Job accessibility decreased by 11.5% in Linn County and 7.2% in Johnson County, disproportionately affecting low-income households and those without vehicles. These findings point to the significance of flood resilience improvement in transport planning, amongst measures such as more durable infrastructure and the use of adaptive routing or temporary transit services that would deliver fair access to inhabitants during extreme weather events.