Trapped?

You remember the scenes after 9-11 of all the stockbrokers and Manhattanites -walking- across the NYC bridges to get away or get home? and how some of them walked ten+ miles in their businessy suits and little ladylike pumps and whatnot?

Well, reading the posted adventures below, I realize something. I'd kind of assumed that the people stuck in N.O. were physically isolated by water and all the bridges down. I knew news people were getting in but sort of figured some were trapped as well and that some were being ferried by boat.

Now it appears that the only thing preventing many people from walking away from New Orleans were men with guns guarding the bridge to Mississippi. What's the deal with that?

I know that they had to keep a route clear for aid, but it sounds like damned little aid was arriving, and surely one lane could have been set aside for pedestrians to leave the scene. If they had siphoned off as many of the able-bodied that were willing to walk out into Mississippi where they could be met and ferried by car or bus to other locations, the task of getting to the ill and elderly would have been significantly less onerous, and what supplies and water were available in the shelters might have gone around much more readily.

It's hard to avoid the implication that they were not allowed to leave because they were black.