Evacuation Route Planner Calculator

When a community needs to move fast, the two numbers that matter most are how many vehicles must leave and how much road can carry them. This calculator applies basic traffic-flow theory to answer both. It first converts your population into a vehicle count by dividing by average occupancy per vehicle (vehiclesNeeded = population / avgOccupancy, rounded up), then compares that against total road capacity, calculated as outbound lanes multiplied by an evacuation-condition throughput rate (roadCapacityPerHour = lanes × vphPerLane). The default throughput of 1,400 vehicles per hour per lane sits deliberately below a road's normal free-flow capacity of 2,000+ vph, reflecting the reality that evacuations run slower than everyday traffic — driver hesitation, merging at bottlenecks, mixed vehicle types, and contraflow confusion all eat into capacity.

Dividing vehicles needed by road capacity gives the clearance time in hours, and adding the drive time to safety (distance / average speed) produces the total evacuation time. The calculator also applies FEMA's phased-evacuation guidance: it recommends staggering departures across a number of waves equal to the rounded-up clearance time in hours, splitting the population evenly across those waves so roads aren't overwhelmed all at once. Treat the outputs as planning-level estimates rather than guaranteed timelines — actual evacuations are affected by weather, accidents, fuel availability, and compliance rates that this simplified model doesn't capture. If your calculated total evacuation time exceeds the warning lead time available, the practical response is adding contraflow lanes or moving up the mandatory departure order, not just hoping traffic behaves better than the model assumes.