To give some specifics: I only remember driving down an actual gravel road (like, for public use) a single time. In 18 years. Even my friends who lived >30min from the nearest "city" (~10k population) had paved roads all the way.
But that is just my own experience. Areas with a different climate or geography might be a totally different story. My hometown area is relatively flat, lots of farmland, and rarely gets severe winter weather.
Not saying it's common. I don't have to drive over one of those but I have had to when there was construction on our regular route. It's right off the main road leading into town from the highway.
> Most of the roads are still unpaved, but you spend most of your driving time on the paved roads.
Yeah I definitely agree with that. I imagine if you were to look at my county's roads from a satellite, it'd be something like the (grid-shaped) veins of a leaf — the thick, prominent veins are the paved roads, providing the structure, while the thinner, branching veins are the gravel roads that run between them.