Roads are NOT going to be built in any kind of efficient way without public funding. Surely, there may be better ways to go about accomplishing the same objectives, but roads are within the community desires about the solution. If you want another solution, besides roads, you have to convince the community to move in that direction. In your rural Tennessee example, that is converting to a less rural existence, the community seems to have decided that it wants more roads.... b/c they see that as the solution to the issue of having more people in the area.
Where did you get "rural" from? Could you stick to what's written? It's a two lane interstate that takes 20 minutes to go 5 miles for mostly unnecessary commutes. There's your central planning.
Yeah... let's get on a tangent...
Frequently, a central reason for adding lanes or roads is a perceived need b/c of population growth or traffic congestion.
I do NOT know about the circumstances or the rationale for the road in your non-rural tennessee location, except for your proclamation (one citizen's assessment) that it was NOT necessary b/c they could have substituted flying cars in that location.
I do NOT want to minimize the importance of your input, but I am sure that there was more than one person that decided that the road was going to be a benefit to the community and that is why it was built. And, also with public projects there are opportunities for community stake holders to comment regarding the necessity or lack thereof of the project.