It depends on the time frame you want to consider. In the 1960s there were few interstate highways and we had no choice but to drive through every town on the highway. I remember driving Route 66 in a 1957 Chevy and going 45-50 mph most of the way. There were a lot of new roads back then and in the 1970s.
Each state maintains their own roads with Federal matching funds. California roads are some of the worst that I ever drive on. I had a new Ford pickup with a TC and frame tie downs. I drove over to CA and dinged up the bed of my brand new truck on the Interstate! I was really pissed off. In the last 25 years or so roads in the West have continued to get worse. Nevada roads tend to be pretty good in comparison.