Assessment of Roadway Flood Severity Using Traffic Mobility Data

Flooding is among the costliest and deadliest weather disasters. Moreover, different types of flooding have significant impacts on the transportation network and infrastructure including flash, riverine, urban, coastal, and storm surge. The variety of flooding scenarios makes it challenging to quantify the impacts of flooding on transportation across spatial scales; however, such metrics would be beneficial both prior to and after the event. Pre-flood metrics can promote enhanced impact-based decision support guidance and hazard communication while post-flood metrics may provide broader consideration of flooding impacts to include larger regional disruptions away from the most inundated areas.

This study explores a multi-faceted approach to assessing flash flood impacts from recent events in 2024 through the use of ground surveys, high-resolution satellite tasking, data collection from broadcast and social media, information from local officials, results from online societal surveys, and traffic mobility data. Traffic mobility data (e.g., speed) are obtained from the Regional Integrated Transportation Information System (RITIS) National Performance Management Research Data Set (NPMRDS) for select road segments during known instances of flooding. Hydrometeorological data are obtained from the National Weather Service (NWS) and includes products such as the Flash Flood Severity Index (FFSI) to quantify the severity of an event, and advisory/warning products to understand the messages that were concurrent with an event. Additional datasets include information such as emergency response (e.g., high-water vehicle rescues) and societal impact surveys to understand which messages were received and what actions were taken.

The assessment of traffic mobility data indicates that there is reasonable agreement between the issuance of NWS flood hazard products and disruptions to traffic mobility. Moreover, in some instances, substantial decreases in speed may serve as a precursor and/or indicator of flooding events that could enhance the overall warning paradigm and ensure that motorists receive accurate and timely information during rapidly changing hydrometeorological conditions. This assessment lays the foundation for future refinement of the FFSI alongside the development of transportation-centric road flood severity metrics as well. The benefits of having such a metric include providing an independent hydrometeorological baseline for resource allocation and asset management in after action reviews, pre-storm messaging and planning will be more consistent and impactful to the public, and stakeholder communications will have greater clarity and conciseness.