Real-time GIS assists hurricane evacuation
South Carolina is familiar with hurricanes. Evacuation route signs dot all of the coastal cities, and few residents can forget the damage caused by Hurricane Hugo in 1989.
Last June, South Carolina Department of Transportation (SCDOT) officials started developing a hurricane management system to manage evacuation and track road usage in a natural disaster. With the help of Intergraph, Huntsville, Ala., officials launched the Hurricane Evacuation Decision Support system just prior to last fall’s notorious hurricanes, Dennis and Floyd. (The latter prompted the evacuation of 700,000 coast-dwelling South Carolinians.)
The system is a web-based presentation of maps that incorporates live information from SCDOT’s GIS, remote traffic counters, evacuation routes, detour maps and real-time weather data. It was designed to put rapidly changing traffic and weather information at the fingertips of state officials who manage evacuations.
Users can combine and distribute digital information from multiple data sources in virtually any type of raster or vector file format and publish the information over an intranet or Internet. Maps can be displayed and queried with any industry-standard web browser. SCDOT incorporated four data types into the Hurricane Evacuation Decision Support system: * vehicle count totals from remote recording devices around the state. Don McElveen, GIS manager in SCDOT’s Mapping and Graphics department, calls that the most important data the system provides. * official emergency evacuation routes from the existing SCDOT GIS; * road closure and detour maps; and * real-time weather information from the Internet.
SCDOT also decided to have real-time weather data linked to the system to provide government officials the ability to compare evacuation progress with the advancing storm and modify the plan accordingly. The system can handle 24 weather data formats, and the data can be displayed as an overlay on the evacuation and detour maps. It also can be time-linked to traffic data to illustrate the interaction between weather and traffic.
With the system in place by late summer, SCDOT had the opportunity to test it during Hurricane Dennis, which threatened, but then bypassed, the state about three weeks prior to Floyd. By the time Floyd was churning the mid-Atlantic in early September, SCDOT had all the details it needed to evacuate the entire 150-mile South Carolina coast.
On Monday, Sept. 13, SCDOT personnel began preparing the Hurricane Evacuation Decision Management System for Floyd, a category 4 storm. The system was programmed to generate three charts from the traffic count data, involving comparisons of: * volumes over the previous five hours; * traffic over the previous four days; and * volumes for the current day, day before, and week before.
SCDOT personnel customized the charts to isolate traffic on specific routes, such as Interstate 26 heading west across the state, or in metropolitan areas, such as Charleston, where many evacuation routes merge toward inland destinations. “The traffic information lets the governor know whether people are leaving in response to an evacuation order, as well as how many are leaving,” McElveen says. “If he issues a mandatory or voluntary evacuation, the governor must get a feel for how people are responding in case he has to change his tactics.”
The password-protected system is housed primarily at SCDOT headquarters in Columbia. During Floyd, command posts in Columbia at the governor’s office and at the state Emergency Preparedness Division were able to access the system via the Internet.
“Our job was to give the Emergency Preparedness Division and the governor’s office the information they needed to make decisions,” says Mark Hunter, an assistant state maintenance engineer for SCDOT. “The challenge is to give it to them in the simplest terms.” Hunter updated traffic counts on the major evacuation routes after the governor issued a mandatory evacuation order to low-lying areas at noon on Tuesday, Sept. 14. At the peak volume late that evening, 80,000 vehicles left Charleston in one hour.
“We kept track of every spot that was having slowdowns,” says Kelvin Washington, an SCDOT assistant pavement management engineer who worked at the governor’s command center. “We could get somebody on the ground, find out what the situation was, then get it cleared up as fast as possible so traffic could continue.”
By late afternoon on Tuesday, the system showed what had most been feared — traffic came to a halt on I-26 outside Charleston because of congestion. That information contributed to the decision to clear eastbound I-26 of all traffic and then re-open it to westbound traffic so that twice as many lanes could carry vehicles away from the coast.
By Friday, Sept. 17, it became clear that the South Carolina coast would not be hit head-on by Floyd. Emergency Preparedness Division officials and representatives from the governor’s office started reviewing the traffic and detour information to see how they might change their evacuation procedures in the future.
