If you look at a map, Gretna is in the opposite direction you want to go if your objective is to get out of the way of Katrina. Gretna is to the south east of NO. You want to go North or West. The only reason to go in the direction of Gretna is to loot
My point exactly
Yes, but north and west were both flooded. From downtown New Orleans, the closest high ground was across the river.
Then, to go west or north, you had to cross back over the river again, and go almost all the way to Baton Rouge. If you don't know the terrain, it may seem crazy, but it's true.
Since you have a map, I can recap for you. From downtown New Orleans, which includes the area of the Convention Center and the Superdome: these areas were completely surrounded by water. The overpasses for the Interstates were above water, but the Interstates themselves were flooded until you got all the way west to Jefferson Parish (area of Causeway Blvd.), then there were some unflooded areas.
North is across the Causeway. The Causeway Bridge was damaged by the hurricane, and is closed.
East is through Slidell. The bridge to Slidell is torn up, and is closed.
West, as I described, was flooded.
From downtown, the bridge to the Westbank was the nearest high ground out of the city.
I still don't have a real reason why people did not walk on the levee to Harahan, but I think it's because of the warehouses and docks. But I do know that some got out that way. It's a much longer route.
The intelligent response would have been for the state of Louisiana to transport these people across the bridge, and then to points west. I have no idea why they did not do this. Private sector individuals had no problem doing this.