Yi-Chang Chiu wants to move people efficiently – lots of people, millions of people – in response to a terrorist attack or natural disaster.

Suppose, for instance, that a disaster occurred in Southern California and suddenly 700,000 vehicles headed for the Arizona border. How would transport officials generate the best traffic management strategy to cope with the traffic?

One very good option would be to use the computer simulation package that Chiu, an assistant professor at The University of Arizona Civil Engineering Department, has been developing since 1995, when he was a graduate student at the University of Texas in Austin.

“Solving large-scale evacuation problems is overwhelming,” Chiu said. “No one can just sit down with a map, draw lines, and figure out the best answer to problems like these.”

No single plan or even series of plans is sufficient he added. “We’re not focusing on a script because a disaster scenario is very unpredictable. You can’t have one plan that fits all situations, and you can’t evaluate hundreds of scenarios or your ‘plan’ will end up looking like a phone book.”

Instead, Chiu and his colleagues have focused on developing software that can react to a situation in real time, adjusting as conditions on the ground change.

“If we’re reacting to a hurricane, we have 72 hours to plan,” he said. “But what if an unforeseen disaster occurs? We need to make a decision in 15 minutes.”

Chiu and his colleagues also have used the software to model what’s called “value pricing” on toll roads. The idea is to use a sliding toll scale to manage congestion. When traffic increases, the toll notches up incrementally to a maximum amount. This information is broadcast to drivers in various ways, with the hope that they will choose a different route, use public transit or delay their trip.

The traffic software, which Chiu and others began building line-of-code by line-of-code back in 1995, has undergone several software engineering cycles since then and now is a mature product that will soon be ready for state transportation and emergency medical agencies.

The next generation of the software, which is now under development, is called MALTA (Multi-Resolution Assignment and Loading of Traffic Activities). It is being designed to run even faster, to handle networks with much larger sizes, and to respond minute-by-minute to real-time emergencies. Instead of running on a single computer, it employs parallel processing, in which several computers work together on the problem.

The National Science Foundation and Arizona Department of Transportation are funding the development and field testing of MALTA.