## 2 Materials and Methods
### Data Processing  
The vehicle trajectory data includes a series of waypoints with the details of vehicle paths within the geographic boundary of three counties: Escambia, Okaloosa, and Santa Rosa. Each waypoint contains detailed information, including geographic coordinates, timestamp, speed, ignition status, and a unique anonymous journey identifier. From 1 to 30 September 2020, there were 2,930,724 journeys with 1,078,927,715 waypoints. Figure 3 is a schematic representation of the journeys recorded during the period under review. Since the data is anonymized, individual trip chains forming a journey are not explicitly declared, meaning that multi-stage evacuations and intermediate stops cannot be directly traced. To reconstruct probable trip sequences, a spatiotemporal grouping technique was proposed, allowing the identification of linked trips based on spatial and temporal proximity. We first define: (1) Start Location (\(x_{s}\), \(y_{s}\)) and end location (\(x_{e}\), \(y_{e}\)) of each trip, (2) Start time (\(t_{s}\)) and end time (\(t_{e}\)) of each trip and (3) Start (\(l_{s}\)) and ending (\(l_{e}\)) ignition status (i.e., whether the vehicle was turned on or off) for each trip. The trips that constitute a journey are matched and considered part of the same journey if it satisfies the following three conditions:  
* Spatial Matching Condition: The end location (\(x_{e}\), \(y_{e}\)) of one trip must spatially match the start location (\(x_{s}\), \(y_{s}\)) of the next trip. * Temporal Precedence Condition: The start time (\(t_{s}\)) of the second trip must be chronologically after the end time (\(t_{e}\)) of the first trip. * Ignition Status Verification: The first journey must end with \(l_{e}\) = \"key-off\", and the second trip must start with \(l_{s}\) = \"key-on\", ensuring a logical vehicle stop before the subsequent trip. Table 1 summarizes the durations of the journeys obtained by the proposed trip chain forming method, summarized by destination county and whether they occurred during the school closure period. The total duration for the recorded journeys/trips is 946,291.2 h. About 6% of the recorded trips ended in counties outside the specified region of interest. The average trip duration within the region is about 0.3 h regardless of the county or the school closure status. However, during the school closure week, the total duration of trips shows a marked decrease (accompanied by a notable increase in the standard deviation) in all counties, as expected. The journeys that ended outside the region of interest have somewhat longer average duration of about 0.45 h. To analyze vehicle movement related  
Figure 3: Schematic of the recorded journeys. to critical facilities (shelters and lodging locations), matched start and end points were intersected with facility ownership parcels. Parcel data was used to ensure accurate facility assignments, including parking lots and designated waiting areas, and reduce false matches that might occur if a vehicle stopped near but not inside a facility. Figure 4 illustrates the start and end points of two journeys mapped onto facility parcel boundaries. To determine vehicle counts, only journeys that ended within facility parcel boundaries were considered, ensuring vehicles that arrived at shelters or lodging facilities were accurately counted. Each journey was treated as an independent event for vehicle count predictions, regardless of multi-stage evacuations, enabling precise aggregation for demand modeling and analysis. By leveraging spatiotemporal grouping, this study partially overcomes anonymization constraints and provides insights into evacuation movement patterns despite the lack of direct vehicle tracking.