Origin of "over-the-road trucking"

I recently learned about the phrase "over-the-road trucking", which is commonly used in the US to refer to long-distance trucking (normally with large semi-trailer trucks) as opposed to smaller trucks making short-distance deliveries.

However, I'm uncertain about the origin of this phrase and how it came to mean long-distance trucking. After all, unless the truck is offroading, all trucking is "over-the-road". Merriam-Webster unhelpfully defines the etymology as:

from the phrase over the road

How did this phrase originate?

The expression over-the-road dates back to the 40s:

1940s; earliest use found in The Sun. (Lexico.com)

It was in those years that the first long distance and interstate roads were built, and the concept of “over the road” conveyed the idea of long distances.

In 1944 – while World War II was still going on – Congress passed the Federal-Aid Highway Act, and committed the nation to building a modern, four-lane interstate highway system across the country. The highway administration mapped out 40,000 miles of interstate.

Trucks. One of the arguments for the interstate highway system was that it would help farmers get their produce from rural areas to city markets quickly and efficiently. Ironically, trucks have never been able to match the low per ton per mile cost of railroads in transporting food. But the speed and flexibility of trucks won the battle for farm to market transportation.

(livinghistoryfarm.org)

Interesting turn of phrase, over-the-road trucking, you wouldn't think it meant long distance driving. In British English “over the road”, without hyphens, would refer to a precise place, e.g. Have you been to the pub over the road? Meaning there's a good pub on the other side of the road.

I must admit to never having heard of its American meaning until today. I doubt I will ever use it, but next time I come across it, I'll know better.

By Googling, I unearthed the following snippets

source: The Termination Report of the National War Labor Board: 1942-1945

November 26 1943
Opinion
The instant case concerning over-the-road trucking was certified to the War Labor Board on November 23 1942. Thereafter it was assigned to the Trucking Commission for hearing and decision A hearing was held on February 5 1943…

An earlier instance was reported in the 1920s, which might indicate how the term came to be coined

On October 9, 1926, in conference with Mr. Albright, he said. “The Cooke road can go to hell as far as I am concerned; as long as Doctor Tanzier operates his trucks over the road I will never spend another cent on it.” I told him that I knew he had a personal quarrel with Doctor Tanzier, but that his attitude was rather hard on the rest of us. He answered “Well that is the way I feel about it.” Doctor Tanzier heads a company that this year has completed a copper smelter in the district.

and in 1927

No other purpose for the road was suggested. My own opinion is that on account of the steep grades and the large number of switchbacks which would have to be made in certain portions of the road, the hauling of freight over the road at the best season of the year would be a difficult task

Driving trucks over the road, suggest a public major road. Wikipedia tells us the plans for building a highway system in the USA was first created in 1922.

In the US, the Federal Aid Highway Act of 1921 (Phipps Act) enacted a fund to create an extensive highway system. In 1922, the first blueprint for a national highway system (the Pershing Map) was published.

From trucks travelling/driving over the road in the 1920s to the 1940s over-the-road trucking the distance was brief.