After Katrina, some people have said that private cars are the only reliable solution for hurricane evacuation. Right now it appears from news reports that all the evacuation routes out of Houston are completely jammed, and that traffic is moving at less than 3 mph. Cars are overheating, breaking down, and running out of fuel.
Personally I am waiting for one of the evacuees to arrive at my apartment. She just called the sheriff's office in one of the counties she would be driving through and was told that traffic on the evacuation route is bumper to bumper (at midnight) and that it would be "faster to walk".
This is days before expected landfall. It is expected that many people in the Houston area will not even begin evacuating until tomorrow.
I think some folks have implied that being carfree is irresponsible because only a car can get you to safety in case an evacuation is required. But maybe cars aren't all that good a solution for emergency evacuation, either. I don't know what the solution would be, though.