While the surplus DC-3’s and DC-4’s did provide low cost transportation, but neither were pressurized. Non-pressurized airliners are limited to 12,500’ msl, which puts limits on when where they could be used in the western US. You want to be 3,000’ above the mountain tops in IFR weather, so no flying near areas with peaks above 9,000’ except in good weather. That’s why Douglas, Convair, Lockheed and Martin were able to sell pressurized airliners despite the availability of war surplus transports.
There’s a big difference between a numbered highway system and a limited access highway system that didn’t become common until after WW2.