Really? Name a couple of cities that were only accessible by foot or horse as late as the 1940s. I'm a history buff, I'd be quite interested in knowing about them.
Right off the top of my head:
Vernal, Utah, didn't even have a stagecoach running to it until a mining company blasted a road for their trucks to get to the nearest railroad in 1938. Which, of course, meant jumping right past horse transport to gas engines. Even then, it was only passable in the summer, and wasn't paved until the road was absorbed during a US Hwy 191 re-routing in the late 1960s / early 1970s.
Be sure to read the little blurb about the "Parcel Post Bank" at the bottom of the Wikipedia page, when you google it. The Uintah Railway, while a mining railroad, was contracted to deliver mail to its own rail towns as well as Vernal. During the summer, they usually used horses for the job. But during the winter, they often resorted to using their tracked tractors or hand carry it on snowshoes. Fresh snow was too deep for horses (and sometimes the tractor(s)) when combined with the nasty terrain. (42 miles each way - as the crow flies.)
Interesting note: The US Post Office paid the railway $1.50 per 50 pounds of goods, but only charged customers a
maximum of $1.08 per 50 pounds of goods. So the railway wasn't happy about their service being delayed for weeks while shipping bricks, but was at least getting paid for it. The Post Office, on the other hand, was furious about having subsidized at least $0.42 per 50 lb on a
35 ton delivery ($588, minimum).