Weathering the Storm

GIS provides a foundation for an evacuation support system in South Carolina.

by / April 16, 2002
The events of Sept. 11 have pushed evacuation planning to the forefront for all levels of government. Among the scenarios being studied are improved ways of evacuating large areas in the event of a catastrophe. Evacuation models for various regions and potential types of disaster are available, and, not surprisingly, GIS plays a key role in the most current of these. In particular, the South Carolina Department of Transportation has implemented a real-time decision-support program for evacuation and has put it to the test under actual conditions.

On Sept. 22, 1989, Hurricane Hugo hit the coast of South Carolina and left a path of death and destruction that penetrated deep inland. That triggered a series of events that led to an operational decision support system by 1999. In that year, Hurricane Dennis provided a dress rehearsal, allowing the state to test features of the system before the hurricane finally skirted the South Carolina coast and skipped away without incident. It was three weeks later, when Hurricane Floyd began to churn the waters of the Mid-Atlantic, that the real test came.

With winds building to a Category 5 storm, Floyd rolled ominously toward the southeastern coastline and South Carolina state officials launched what has been called the largest peacetime evacuation in U.S. history. From Beaufort to Myrtle Beach, more than 700,000 people streamed onto the highways to escape inland. As emergency personnel along the 150-mile coastline began the evacuation for what might have been the worst natural disaster in the state's history, they worked with up-to-the minute detailed information provided by South Carolina's Department of Transportation (DOT).

In the end, Floyd fell flat, blowing itself out at sea and making an innocuous landfall. But the system worked. Those who had to leave the coastal areas got out in time. Of equal importance, the data made available by the experience provided a solid basis for evaluation and refinements that would make the next evacuation go even more smoothly.

Integrating Existing Data Sets

"The system basically integrates and displays up-to-date weather data with real-time traffic data taken from sophisticated induction strips that are built into the pavement," said Rob Mott, senior technical manager with Intergraph, which assisted the state in developing the GIS components of the evacuation system. "These air-pressure tubes record traffic counts and are in place at more than 150 locations. This system was already in place, so it was ideal for collecting data in connection with the hurricane evacuation system."

According to Mott, the evacuation support system makes traffic counts available via the Web to the operators at the DOT. Using historical information about traffic flow and road capacity, these operators can assess how an evacuation is proceeding. They can also determine how much time is left before the storm makes landfall and locate the most critical areas of potential threat. Using this information, other state officials can implement a variety of strategies designed to minimize traffic jams and speed the evacuation process.

For example, traffic can be rerouted to avoid tie-ups or bad road conditions. Additionally, traffic lanes can be reversed, so lanes that would normally be used to go toward the coast can be opened up to double traffic capacity away from the coast.

The real time weather data is presented in pictorial form. It is not dynamic, but rather a snapshot that shows coastlines, highways and terrain features. Because hurricanes come in with a very distinct cloud formation, it is easy to see where the front is, and that pictorial information is useful in giving perspective to the traffic data.

Simplified Information Distribution

To combine and distribute digital information over the Web, South Carolina's DOT is using GeoMedia Web Map, a Windows-based software suite that accepts and publishes multiple data sources over a network. Maps can be displayed and queried with any industry-standard Web browser. As a result, personnel did not have to learn any new software in order to access and use the system. Standard road maps are scanned into the system and used to show officially designated hurricane evacuation routes, road closures and detours around closures.

"In the two years since Hurricane Floyd, we have made a number of enhancements," Mott explained. "Most of these have to do with improved performance and upgrades to the latest version of the Web Map software. We have also restructured some of the underlying databases for improved performance and moved out of spreadsheets and into a relational database for richer reports and better integration."

The move to a relational database supports queries across time and allows different types of data to be generated.

"With the enhanced systems, operators can look at the actual traffic counts to see how many vehicles are moving through each lane on an hour-by-hour or an on-demand basis," said Mott. "The user can also look at the number and graphically compare it to counts of a day ago, a week ago or longer. The end result is the data is available in a format that facilitates faster and more reliable ways to make crucial decisions."

Flexible for Future Systems

The South Carolina system has been specifically designed to support decision making for hurricane evacuation, but Mott believes is can easily be applied to other evacuation scenarios. "The software in place is user-friendly in terms of putting in other types of data," Mott explained. "It is very flexible and allows different departments to represent other types of features."

Sites of interest can be highlighted, for example, and buffer zones of various radiuses can be displayed. With any evacuation support system, traffic counts would be a critical data set, and that capability is well represented in the South Carolina example. Complementary data sets useful in real-time decision support, such as additional maps and historic traffic trends, could also be included.

"We have also used color coding," Mott noted, "to indicate areas of particular concern and to make it easy to communicate among various users about where to focus our attention to get people out as quickly as possible."

In addition, various intelligent agents have been added. For example, as an operator rolls a mouse over the map, information is displayed about a segment of highway or a specific traffic count. The user can then click on that and drill down to get a report. "It's very intuitive, very flexible with a lot of intelligence behind it," Mott said.

No one ever wants to have to use an evacuation support system. But disasters of all kinds do occur, and proper planning can make the difference between an orderly and safe exit and a catastrophe.