Only time will tell, but we may be near the end of the road building era in the U.S., and probably in Sonoma County as well. Nevertheless, there is a huge road infrastructure accumulated over many years that has to be maintained in perpetuity.
In the U.S., and to a lesser degree elsewhere, road networks evolved into a hierarchy of roads specialized by function:
||direct property access
||gather traffic from local streets and feed it to the arterial system.
||longer distance mobility and not intended to serve as immediate access to properties
||fully grade-separated so no signals are required for traffic on the freeway. No direct access from property.
At the same time, where the street networks were once mostly a grid structure, they became more dendritic, or "tree-like", tending to force more traffic from local to collector to arterials, thereby causing the arterials to become congested.
Then came TND, or Traditional Neighborhood Development. A decade ago, Walter Kulash, one of several notable traffic engineers associated with the traffic aspects of TND, explained Why TND Traffic Systems Work.
Sonoma County's rural roads are beautiful, yet sometimes hard to enjoy, especially from a bike or on foot. Creation of a system of Heritage Roads might be one solution.
City streets can be made better for all users. Seattle published an informative guide a few years ago, Making Streets that Work, which you can download in PDF format (2.6 Mb).
Environmental impacts of increased road capacity
Implicit in the concept of installing HOV lanes to widen a freeway is the assumption that pollutant emissions will be reduced. Recent studies bring that assumption into question.
How will a road "improvement" affect air quality? A central question is how emissions change with traffic speed. For many years there has been an expectation that moving the traffic along faster will help reduce pollution. Well, yes, it was too good to be true. Read John Holtzclaw's article on how emissions change with traffic speed, in the Sierra Club's SprawlWatch website.