Analyzing evacuation route choices during the 2021 Marshall Fire

Knowledge of household evacuation behavior in wildfires is critical to creating effective emergency plans. Understanding evacuation route choices is especially important for both evacuation management strategies and traffic simulations during emergencies. Existing studies of evacuation route choice rely solely on survey or interview data, which have inherent limitations in spatiotemporal resolution and memory bias. This study proposes a new methodology to analyze evacuation route choices and complement existing data sources by leveraging a GPS dataset. The proposed methodology includes a framework for systematically handling sparse GPS data and testing common assumptions used by existing evacuation simulations, i.e. whether evacuees take the shortest path, make a single trip to their destination, or are at home at the start of the evacuation. We applied this new method to a sample of 155 evacuees from the 2021 Marshall Fire in Boulder County, CO, which resulted in the evacuation of over 30,000 people. We found that the majority of evacuees approximated the shortest path (67.1%), made multiple trips while evacuating to their final destination (64.7%), and were home at the start of the evacuation (60%). The findings of this study can be used to inform better plans for future emergencies and enhance traffic simulations of evacuation behavior. • Introduces a GPS-data-based method to study wildfire evacuation route choices. • Tests common assumptions about evacuee behavior used in existing simulation models. • Finds 67% of evacuees followed near-shortest paths, 65% made multiple trips, and 60% started from home. • Provides insights to improve emergency management and evacuation traffic simulations.