Hurricane evacuations have long vexed emergency officials. Figuring out where a storm will hit is a sketchy bet 24 hours or more in advance, and many locations require at least that long to complete an evacuation.

A new approach could save lives by getting certain groups of people, such as tourists and the elderly, out first.

Waiting too long to evacuate people can have disastrous effects, as seen in 2005 with Hurricane Katrina. On the other hand, ordering too many precautionary evacuations can lead to one of hurricane official's worst fears: complacency the next time around.

But there is another problem that few emergency plans consider: Poorly planned evacuation can cause roadway gridlock and trap evacuees in their cars, as occurred with Katrina and Rita in 2005.

MIT graduate student Michael Metzger has used historical hurricane records, mathematical models and other scientific considerations to come up with a completely different way of looking at evacuations.

Metzger's new formula calls for evacuating an area in stages, while focusing on different categories of people rather than different geographical locations.

Metzger suggests the elderly might be evacuated first, followed by tourists, families with children, and then the rest of the people, a process phased in over two days. With his system, officials could "pull the trigger earlier, and phase the evacuation," Metzger said this week, and thus potentially save many lives.

The idea has been viewed favorably by federal and state emergency officials, according to an MIT statement, and the U.S. Department of Homeland Security earlier this year awarded Metzger second place for the research in a competition.

Coincidentally, Metzger points out, a modest version of this approach was implemented successfully this month when hurricane Fay struck Florida: Tourists were asked to leave while many residents remained. Already in New Orleans on Saturday, some residents were fleeing New Orleans in the face of a possible strike next week by Hurricane Gustav.

Other factors that could help to make evacuations more effective, Metzger said, include making sure transportation modes are ready, better planning for where evacuees can go, and preparing supplies in advance at those locations.

Metzger's approach "embodies elements of engineering, management and the social sciences," said his adviser Richard Larson, an MIT engineering professor.