
Busing had been tested in the Hurricane Pam simulation of September 2003, and it was found that the problems and risks were much greater than the possible benefits. They planned another simulation to work out all the deficiencies revealed by Hurricane Pam, but it was canceled because the Bush administration killed the funding. One of the biggest problems was finding shelter for all those infirm, aged, children and penniless black people. No one wanted to accept them in the northern Louisian counties. They would have had to send them out on the road looking for shelter in slowly crawling traffic and oppressive heat and humidity. As it turned out, this was, indeed, very risky.
http://www.ammachi.org/humanitarian-activities/get-involved/Katrina/update-from-centers.html
"The Oklahoma Affiliate Center has been assisting survivors at Camp Gruber (a military camp where 2000 people were bussed from the superdome in New Orleans). The survivors arrived at 10 p.m. Saturday night wearing the same clothes they wore when the hurricane hit. They had been on the Greyhound bus which first went to Houston, where they were turned away, then to Dallas, and arrived at Camp Gruber thinking they were going to die on the bus, because no one would take them in. Some did die on the bus, many died and were killed in the superdome, and they were in shock from all the trauma."
As you may be aware, the sheriffs of the parish across the Mississppi river from the Convention Center turned back a group of about 200 evacuees who tried to cross the bridge. They evacuees say that the officers fired over the head to dissuade them. This is not a rumor. The sheriff of Gretna was interviewed on TV about it. So that does tend to explain the general attitude that the New Orleans disaster planners faced. Therefore they decided long before the storm to use the shelters of last resort, after having been assured by FEMA they could expect rapid relief. The shelters did protect the people from the storm. The relief arrived a bit late.