Evacuation Routes

An evacuation route is a roadway or path designated for use before or during a hazardous event to move people to safety. Evacuation routes may be designated [Page 192]for use during impending tropical cyclones, tsunamis, river floods, wildfires, volcanic eruptions, earthquakes, chemical/nuclear disasters, or other hazards. Evacuation routes are designed to safely move as many people as possible in the shortest time and over the shortest distance to locations away from the danger. It may be desirable to have some form of sheltering and provision of food, water, and medicine along the route and at the destination.

Evacuation routes are planned using knowledge of the areas and populations at risk. Maps are constructed for specific hazards, such as the areas flooded by a given tropical cyclone storm surge, an expected river flood crest, the path of a volcanic lahar (volcanic mudflow), or potential burn areas at the wildland-urban interface. The large-scale maps are created from census data about local populations and from meteorological and geophysical experiences from past events and the landscapes known to be at risk. In the developing world, local knowledge is used where other data are not available.

After maps of the relative risks are produced, they are distributed as paper maps or digital maps online. The local population is made aware of the risk maps and the location of their homes and daily activities with respect to the risk zones. When a hazardous event is expected, forecasts are made of the magnitude of the event, the forecast (the height of storm surge, for example) is broadcast to the public, announcements are made about the areas that should be evacuated, and residents use evacuation routes to escape the hazard zones.

To be effective, the existence and location of evacuation routes should be known to the population at risk, be well-marked, and lead to a destination that reduces the risk of injury and death to the evacuees. Evacuation routes can be designed using geographic information systems (GIS) that incorporate the shortest-path algorithms with information about the road network, highway elevations, traffic volume and flow speed, and behavior of drivers during the evacuation. Route planning is computationally challenging because the transportation network may be very large and the number of evacuees often exceeds the highway network capacity. Standardized signs that are hazard-specific are used to mark evacuation routes.

Government officials may issue a recommendation for occupants of a hazardous zone to evacuate to a safer location, or they may issue a mandatory evacuation order. Even if a government mandatory evacuation order is not given, occupants of a hazard zone may choose to evacuate. In addition, persons outside of the hazard zone may evacuate through poor understanding of the risks or by exercising extreme caution. Voluntary evacuations from outside of the hazard zone are called shadow evacuations. Officials hope to avoid shadow evacuations because those evacuees add to the traffic flow and slow the overall evacuation.

Evacuation of special-needs populations, such as the elderly and mobility-impaired, present special challenges; they often require adapted vehicles, mass transportation, in-transit medical care, and a destination at the end of the evacuation route that is adapted to their needs. Facilities such as hospitals, nursing homes, schools, sports stadiums, shopping malls, and jails must be addressed individually when planning evacuation routes and methods.

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