Other nightmares can include having not enough gas to get out of the city, but clear freeways due to contra flow; all kinds of bad things happening (unable to evacuate hospital and nursing home patients) because emergency personel could not enter the city; too few police because they are trying to manage the contra flow rather than evacuating people and maintaining order; etc.
I don't know what is best, but I do know that they've usually done some thinking about these kinds of issues in disaster planning. And every choice has it's faults. I just don't feel comfortable saying they're complete idiots not to have put contra flow into action earlier without understanding the whole system. I can easily see several problems with doing contra flow, and I'm sure there are many more that disaster planners are familiar with.
They're up against human nature (hoping the hurricane will miss, delaying to get another day's work in, another day less of hotel stay, denial, etc.), and nature itself, and it's not an easy task.