Hurricane Evacuation Time Calculator
Estimates total evacuation time considering distance to safety, population size, available road capacity, vehicle occupancy, and storm approach speed.
Formulas Used
1. Evacuating Vehicles:
Vehicles = (Population × Compliance%) ÷ Vehicle Occupancy
2. Total Road Capacity (vehicles/hour):
Capacity = 1,800 veh/lane/hr × Lane-Miles × Contraflow Multiplier
(1,800 veh/lane/hr is the Highway Capacity Manual standard for freeway capacity)
3. Network Clearance Time (hours):
Clearance Time = (Vehicles ÷ Capacity) × Hurricane Category Factor
4. Travel Time (hours):
Travel Time = Distance ÷ Effective Speed
Effective Speed = 35 mph ÷ Category Factor
(35 mph is the FHWA-observed average evacuation speed under congested conditions)
5. Total Evacuation Time:
Total = Clearance Time + Travel Time
6. Safety Buffer:
Buffer = (Storm Distance ÷ Storm Speed) − Total Evacuation Time
7. Recommended Order Lead Time:
Lead Time = Total Evacuation Time + 2 hrs (mobilization/preparation)
Assumptions & References
- Base highway capacity of 1,800 vehicles/lane/hour per the Highway Capacity Manual (HCM), Transportation Research Board.
- Average evacuation travel speed of 35 mph under congested evacuation conditions, per FHWA Evacuation Traffic Management Guidelines.
- Contraflow operations increase effective lane capacity by approximately 40%, consistent with post-Katrina FHWA studies.
- Hurricane category congestion factors (0.85–1.20) reflect increased demand and behavioral delays as storm severity rises, based on FEMA Comprehensive Preparedness Guide (CPG) 101.
- A 2-hour mobilization/preparation buffer is added to the recommended order lead time per FEMA CPG 101 v2.0.
- Compliance rates typically range from 70–90% for mandatory evacuations (Baker, 1991; Dow & Cutter, 1998).
- Average vehicle occupancy of ~2.5 persons/vehicle is consistent with U.S. Census American Community Survey household travel data.
- This calculator provides planning-level estimates only. Official evacuation decisions must be made by emergency management professionals using real-time traffic modeling tools such as CEMPS or ETAP.