Lots of things are in fairly close proximity to highways, this is not really a solution. Crashing into the tower block next to a highway is still pretty bad.

Lots of things in dense areas also are not necessarily on an easy route near a highway, so if that's the limitation you run into Concorde's old problem of "where can you actually fly this thing?"

I'm skeptical about the rest of it, but the article lightly covers using existing transport corridors (waterways, rail tracks, and to a lesser priority arterial roadways) as routes for these medium-range flights that explicitly avoid populated areas.

My issue with this is that most transport corridors are

1. not very wide in the first place. Any air vehicle could cross the width of your standard rail line or highway or river in seconds.

2. Surrounded by intensive land uses, because the transportation corridor itself provides valuable access. So vehicles don't have to go very far off the right of way to crash into something valuable where lots of people are.