Rob,
Figured it out. And old GTW line used to go through there, so that's why there is nothing on the northside of Longway.
This line serviced Chevy in the Hole and went right through the northern end of downtown. In fact, I think this is what Union Street is named after as the GTW line crossed diagonally the Pere Marquette line immediately north of the northwest corner of the old Citizens Bank Building:
You can see why they moved these lines. That must have created a heck of a lot of congestion when trains would have to stop downtown at the junction.
Anyway, I wouldn't be surprised to find that CN (successor of GTW) still owns the right-of-way north of Longway. And here I was thinking this empty land was the result of an urban renewal scheme gone wrong and that there used to be a commercial strip there. lol