Between NO and surrounding parishes, there were something like 2,000 school and transit buses. With 60 passengers each that's about 120,000 people who can be evacuated in one trip. It was in both the NO city and LA state plans to commandeer transport from various government entities like school districts to evacuate residents. If regular drivers had left, the governor could have ordered national guard units to drive. If an 18 year old who had never driven a large vehicle before could drive a shool bus to Houston, why not members of the national guard?
The 18 year old was 20, and he drove out two days after the storm. Great story though. There was no capacity to get drivers from anywhere to drive those buses in a timely way before the storm, absent the US military getting on the move immediately.