To live in New Orleans is to leave New Orleans at regular intervals, traveling light: three days of clothes, a cell phone and insurance papers, maybe a lap-top, a six-pack, a pet. The car, kept perpetually gassed up from June through September, encounters gridlock and inches on, west through Baton Rouge or north to Jackson, creeps through the night to whatever friend or room awaits. When the storm makes landfall, the car returns on roads less dense,...