NCPA - National Center for Policy Analysis


October 7, 2005

The chaos caused by recent mass exoduses show that officials have a lot to learn about optimal evacuation strategies and that few decision makers know the science of evacuation, says the Wall Street Journal.

To increase outbound flow, city officials implement contra-flow -- or the opening of both northbound and southbound lanes of traffic; this method will increase a road's capacity by 60-70 percent. But to further increase flow, officials must also convert other traffic aspects, says the Journal:

  • Entrance ramps on the reverse lanes must be converted to exit ramps, so cars can drain off the freeway and keep traffic moving.
  • Police should be posted to keep vehicles from entering contra-flow lanes and officials must change the flow on crossroads and feeder roads to carry traffic away from the freeway.
  • Using secondary roads as adjuncts to highways requires changing traffic signals to give priority to evacuees; but traffic signals are controlled by the state and the municipal court, so officials must coordinate the two systems.
  • Build turnouts on medians so out-of-gas vehicles can pull over and stage departures by Zip Code to reduce traffic.

Whether people wait their turn to evacuate is an open question; that's why computer simulations are crucial to emergency planning, says the Journal:

  • They show the consequences of a mass exodus and other situations.
  • They let officials practice the mental nimbleness crucial to thinking under fire, and seen when their natural reactions backfire.

Simulations also show what happens when assumptions implode; many hospital emergency procedures for disasters assume the presence of police to keep order, but what happens when the police are busying trying to control traffic?

Indeed, if there is no warning, getting people out of harm's way is just not in the cards, says the Journal


Source: Sharon Begley, "Modeling, Simulations Can Help a City Offer More Efficient Exodus," Wall Street Journal, September 30, 2005.

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