[bobthepanda]

It costs a lot to modify an existing street vs build a brand new road, mostly because you have to modify drainage (Loop Link had concrete boarding platforms in the middle of the street that certainly would've disrupted existing drainage), bring the street up to modern standards, and keep the existing street open during the work for all the buildings that front it. It's really not all that simple.

In fact, the fact that it was on an existing street would make it very expensive to modify; look at a picture of the O-Bahn and there's plenty of space for construction vehicles and staging to set up, no one to get in the way of, etc.