There have been at least 3 different photos with buses sitting in water up to their eyeballs, with counts surpassing 570. That's just school buses. In addition, Don't-Blame-Me Nagin had authority to call on the 367 Rapid Transit Authority (around-town) buses, plus 36 "special needs" (handicap-equipped?) buses, plus 26 additional contract buses, all of which sat unused and flooded out. But none of them would be as plush as the Greyhound lines, certainly.
Let's not forget that with Bush declaring a national emergency before the storm that if Louisiana had also declared a mandatory evacuation on time they probably also could have ordered AMTRAK to send a train into New Orleans on Saturday and maybe even on Sunday to evacuate people.