According to my parents, some US routes were still gravel in 1960s in southeastern Ohio headed into West Virginia. Where I grew up in Ohio, all the US and state routes were paved (no interstates there), but some county roads were still gravel. Most township roads were unpaved. I haven’t lived there for thirty years, so it’s likely more paved now. But winter freeze-thaw cycles destroys roads quickly. Gravel roads are cheaper to fix.
When I was growing up in the Eastern suburbs of Cleveland, there were still a few public brick roads. They were covered by asphalt sometime after IO got my driver license in 1965. The only gravel roads I was aware of were far out and seldom used – usually dead ends.
Depends what you mean by paved and where. Assuming the US, Confederate soldiers in Lee’s forays north in 1862 and 1863 remarked on how major roads in MD and PA were ‘paved’ but that meant macadam in the original sense*, self binding crushed stone, what would be called a gravel road now. But that was in contrast to almost strictly dirt roads in the South.
In between that and hot mix asphalt roads were various systems of spraying a binder on gravel roads, some kind of oil or asphalt (but not laid down as a mixture of stone and asphalt like a truly modern road). There are still roads like that in some rural areas even in the northeast, I was driving on one in PA not that long ago, signs noting ‘recently oiled’ or something like that. The car doesn’t throw up as many stones and in places you can hardly tell you’re not on a hard surface road, though in other places you still can.
Hot mix asphalt and concrete roads for state and federal highways corresponded roughly to the large scale adoption of cars. There were cars and hard paved roads ca. 1900 but few of either (~8,000 and ~4% of roads). Both rapidly grew thereafter though cars got a bit of a head start ~8 million by 1920, which is when hard paved major roads began rapidly replacing gravel ones. There were around 30 million cars by WWII and the great majority of state and federal highways hard paved by then, though most lesser roads still were not.
Even today only around 60%-2/3’s (depends who is counting) of US road mileage is hard paved, and in places like the Dakota’s it’s the other way around, 2/3’s or so gravel, by mile of road, though dirt roads have become a small %. But if you weight by traffic density of the 200+ mil cars, paved roads are the overwhelming % in the US and still the bulk even in sparsely populated states.
More road trip anecdotes, you can’t get from the main east-west highway in northern Montana, US-2, to I-90 in the middle/south without leaving paved roads, at least in a big portion of the eastern part of the state. I wanted to, but didn’t think prolonged gravel road driving was a good idea in my car, low slung though AWD. But it’s pretty unusual in most other places even in the West not to be able to a take a general direction because of lack of paved roads. You might have to take a gravel road to get to a particular person’s house or perhaps particular attraction (we did do a couple of hours of rough gravel road driving to see the Pawnee Buttes in NE Colorado, a BMW 328 can do it, but doesn’t like it :)) but not to go a particular general direction. No problem going where we wanted in remote parts of SD/ND on paved roads, though loads of gravel roads in those states.
*not macadam as a synonym for a mix of asphalt and crushed stone as the term is sometimes still used now.
As late as the early 1970s there was at least one named street in St. Louis that was just crushed rock. Granted it wasn’t much of a street - maybe 100 feet long, but it had a name, stop signs at both ends, and was listed in directories.
There are still plenty of gravel roads in rural areas.
The argument for the Interstate as a defense measure came from a test in which anArmy convoy of 81 trucks traveled the Lincoln Highway from Washington DC to San Francisco. It took them 62 days (6 were days of rest).
Most of this can be traced back to bicycle groups in the late 1800’s like the Good Roads Movement to start with although bicycles were not the cause of the massive scale later.
The Good Roads Movement inspired roads like the Lincoln highway. The Lincoln highway caused a huge economic boom for communities that were next to it which encouraged more and numbered highways replaced auto trails in 1926
The cold war and the Interstate system started in the 1950’s. These federal highway funds are what lead to the infrastructure existing to apply asphalt at a lower local cost. The invention of mechanized machinery like the Caterpillar Auto Patrol in the mid 1930’s also helped reduce the costs.
While there are a dozens or thousands of reasons and exceptions, federally funded highways and the rise of the automobile caused the initial build out and then it became an expectation and point of pride in many areas. In some states like Wyoming which have major cross country trade routes ~68% of the states Federal aid is in highway funding.
In some locations of the country like the pacific north west, where Oregon was an early user of asphalt west of the Mississippi it was forced due to roads becoming impassable by cars due to mud during the wet season as an example.
But the short answer for the OP, bicyclists pushed for it first then the automobile came making it practical and desirable and the cold war funded most of it.
Or go up to Duluth, where a couple decades ago they re-bricked some of the major streets in the downtown area (Superior Street and in Canal park). They had some extra money leftover from building I-35 so let’s spend it! Now 20 years later the bricks had deteriorated and they just finished rebuilding the street with concrete.
The road running past my grandparent’s house was gravel/shale up until 1968 or so - I remember watching it get paved when I was a little fellow. It wasn’t a highway, but it did directly intersect with a state highway.
When they dug up a road in CBD sydney, they dug up an old wooden roadbase… made of planks (not sawdust or other fibre). The road was sloped so I guess it prevented washouts and so on.
Well you see CBD’s have had paving since the bronze age, and the romans built long roads, but they weren’t sealed.
So the modern idea is sealed roads, as unsealed pavers/cobble stones/bricks will always sink , or wash out, and become unstable and be filled with puddles and can only be low speed .
If the question is, when did sealed roads become normal ? Well depends on what you are talking about… the sealed roads spread out from the CBD into high density suburbs nearby, and During the 40’s and 50’s for most of the city out to the regular home suburb. A bit later for the towns and communities outside of cities. There’s no date for acerages…which is a heck of a lot of the population of the USA… are most on gravel roads still ?