re: Could they build an overpass interstate on top of Airline Hwy?

It makes more sense to do this on Airline from I-12 to Florida Blvd, and then make Florida an interstate all the way into downtown where it would cross the river on a new bridge next to the Horace Wilkinson bridge and connect with I-10 on the Port Allen side.

It would tie into I-110 and could utilized the existing Wilkinson bridge so that the project could be completed in stages (2 generations if history is an indicator).

Best part about this plan is a good deal of Florida Blvd is wide enough to put it at ground level with feeder roads. You could also expand Florida east bound as limited access freeway out to Denham Springs and beyond, at least across the Amite River.