I'm jumping in a little late here, but this is an interesting topic to me. From a professional standpoint I do a fair amount of work trying to preserve trees on public and private construction projects.
I'm fortunate to work in communities where these efforts are valued—that's certainly not always the case! And I have also learned a lot by collaborating with engineers and architects on these various projects...
When I get into these conversations there is the realization that we have inherited our infrastructure situation, and we live in a time where there is great opportunity and need to do things better. I can imagine a time when many of our existing roads may simply become obsolete—for a variety of reasons.
Population growth, changing climate, and dwindling fossil fuel resources will force our hands. If I was a betting man, horses and buggies might be a growth industry once again. : )