Washington ? Ask any hurricane expert, any disaster planner. Or ask anyone who knows about evacuations and he’ll tell you: There are always some people who stay behind. During Hurricane Elena in 1985, 10 percent of the inhabitants of the washed-out coastal barrier islands refused to leave, despite repeated warnings and despite their relative wealth. They stayed because they had lived through hurricanes before; because they believed, incorrectly, that their homes were impervious; and because – surprisingly often – they were worried about their pets.

Quite a few also stayed because they “didn’t hear” the warnings to leave. Jay Baker of Florida State University found after Hurricane Charley last year that at least half of the people who stayed weren’t aware that they were supposed to leave, despite media coverage and a mandatory evacuation order. Another researcher, Carnot Nelson of the University of South Florida, found that after Hurricane Elena in 1985, people were far more likely to leave if they had heard an evacuation order from an actual person, walking through their neighborhood or knocking at their door.

Still another, Mike Lindell of Texas A&M, thinks the best measures are even more dramatic. He tells, approvingly, the story of one local official who goes through neighborhoods likely to be hit by a hurricane and asks those refusing to leave to fill out a toe tag, the better to identify their bodies after the storm.

In New Orleans, as we now know, the numbers who didn’t evacuate were multiplied dramatically by the city’s unusual immobility: Some 57,000 households in Orleans Parish did not own a car. A University of New Orleans study published in July noted that only 48 percent of the inhabitants of Orleans Parish had a definite evacuation plan. Susan Howell, one of the study’s authors, says emergency managers knew of this immobile population and had discussed them, inconclusively: “There was no comprehensive plan to get them out.”

The city made no provision either for the people who wouldn’t leave or for the people who couldn’t. On the day before the storm, the “mandatory evacuation” was announced over the radio – but there were no officials delivering a personal message, let alone distributing toe tags. The interstates out of New Orleans were turned into one-way roads – but there were no buses, trains or ships for those who couldn’t drive. The city initially won praise for evacuating some 80 percent of 1.4 million area residents, but no provision – in the form of rations, water bottles, security – was made for the 25,000 people who showed up, predictably, at the Superdome, the city’s designated “shelter of last resort.”

This failure is worth remembering and retelling, not only to better understand what happened last week but also because it goes to the heart of what’s wrong with all of our “preparedness” exercises: Emergency planning, much like academic economics, too often assumes that human beings will behave in a rational manner, that they do what they are told, and that they are more or less middle class.

Go to the Department of Homeland Security’s Web site at www.ready.gov, and you’ll find lots of useful advice (“If you have a car, keep a half tank of gas in it at all times”) geared almost exclusively toward people who are going to leave town anyway. The D.C. Emergency Management Agency’s Web site tells you, among other things, to “take photographs or videotapes of your belongings,” and advises that “at least one telephone in your home should be a regular touchtone device.” It doesn’t say what to do if you don’t own a telephone – although in that case, you won’t be reading anything online anyway.

If we have learned one thing from the Katrina experience, it is that all this advice must now be rewritten, and that information must be redirected at the immobile, the unwilling and the distrustful. This means rethinking not just the preparedness Web sites but the whole subject of disaster planning.

After all, the 125,000 people who didn’t leave New Orleans are the same 125,000 who won’t get vaccinated in the face of a mass epidemic, who won’t stay inside in the event of a chemical attack and who won’t do what they are told after a “dirty bomb” is detonated outside the White House. They are the same 125,000 people who will always require food, water and, above all, security when everyone else has fled.

I doubt many disaster planners have thought much about this population. As of Friday, a spokesman for the D.C. Emergency Management Agency could not say how many District households don’t own a car. From now on, that is a number that should be known to every person who works in that department, and to every emergency planner across the country. That is the bare minimum number of people who will always be left behind, and who will always be the public’s responsibility. It’s time to move them from the periphery of emergency planning and toward the center.