In my town, before the Interstates were put in, the county/state transportation departments bought out and set aside strips of land in the 1950s and kept them empty for 20-30 years until construction started in the 1970s. Trees grew in during that time while the land around it got built up. It's weird looking at maps and aerial photos from that time period and seeing empty space. They would have become cool little wooded areas if the highways were never built.

I'm assuming the same happened in New Orleans in the "before" picture: the highway was planned and the land was bought out well in advance, and trees grew in during that time.

I also thought the trees was the after not the before, but the comments said otherwise sadly