I just found it odd that traffic flowing in on I-10 was one or two vehicles while there was a traffic jam flowing out. I would have used at least one lane of the inbound as outbound like they do in cities for football game crowds.
http://www.freerepublic.com/focus/news/1473742/posts?page=27
More pics of Slidell
That was supposedly done although I never saw any video of anything other than what you described.
It's a bit harder to do that in an urban area where there is a concrete divider between the lanes instead of a grass median with perhaps a wire or steel guardrail. I doubt that there was a pre-cut section available in the areas where the camera were. Also, it takes time to set up a barrier (more for a semi-permanent one; less for barrels, but the barrels would need to be picked up before the wind picked up).