That may be true in many cases. But I distinctly remember some of the highways that were built in Portland, and they bulldozed existing suburban neighborhoods to do it. This city was basically one big suburb well before someone had the bright idea to build I-5 through downtown. Heck, almost all of the [residential] tall buildings in the downtown area were built well after the freeway was built.

We have an urban growth boundary now which tries to limit further sprawl, but it can't change the fact that the Portland metro area is 2 million people most of whom live in single-family homes, or maybe low density suburban apartment complexes.