"Somewhere between 80% and 90% of New Orleans evacuated before Katrina hit. I call that a successful evacuation."
So do I.
IN hindsight, in both situations, people took it upon themselves to evacuate based on the forecast available. I'd be willing to bet that more than half the New Orleans population was out of town before the mayor even mentioned evacuation. Houston and Galvaston called for Evac sooner, and so people probably hadn't gotten such a head start on the government as they had in NOLA.
The real difference was that the cities in Texas made arrangements and strong efforts to get those unable to get out a means to evacuate - that was not present in NOLA and represents the major difference between the two.
IMHO, both situations show inadequate road infrastructure to be able to move such large populations and their personal effects out of a city in a timely fashion. We either need more roads, or lower population density.