Often, people who are safe and far away from a disaster zone will look at the victims on TV and wonder: Why they didn't leave? Yes, sometimes it's bravado, or stubornness, or disbelief (expecting another false alarm), or a desire to protect their belongings. But in the case of New Orleans before Katrina, there was another problem: People were told to evacuate the city, but given no means to get out except their own cars. And a lot of people don't own cars.
Maybe they were poor, or elderly, or disabled, or in some cases not interested in the costs and obligations of owning a motorize vehicles. Some were tourists who didn't happen to rent a car, because they were in an urban area where it was cheaper to take public transportation and cabs. But it appears that the New Orleans disaster evacuation plan simply told them to get out of town. If they didn't have the means or money to do so, they were left behind.
This is what happens when a society becomes so auto-centric that the natural assumption is everyone must own their own private vehicles. Roads out of the city were jammed for hours with all those private cars; but many other residents were forced to suffer the grave dangers of a life-threatening storm in a below-sea-level city because they didn't own an automobile.
In major urban areas, a reasonably high percentage of people don't have cars or immediate access to cars. It seems to me we need to look at that issue as we're doing Homeland Security planning.