It seems to me that there should have been some traffic controls. It should have been possible for those leaving the city to use some of the incoming lanes since they were not in use. It would not take much work at all to make that happen.
Louisiana had the Contraflow lanes open by 4:00 p.m. on the Saturday before Katrina.
On-ramp metering is more important than opening the reverse direction lanes. The capacity of a freeway is a function of the average vehicle speed. It's better to keep cars queued on side streets rather than turning the freeway capacity into a 1 mph virtual parking lot. They could have evacuated 100 times faster with one metering traffic cop posted at every on-ramp.