Unfortunately the Interstate Highway was public and paid for by the US government as part of a larger goal of decentralizing production (less chance of it all being taken out by a Russian nuke) and promoting suburban development. The privately owned railways couldn’t compete. Nobody actually planned this; it was just the natural response to the provision of cheap fast roads.Reality is more complicated than that, and railroading is well suited to wholesale movement of containers from dockside or factory to warehouse, less so for the retail movements.
And we all have to live with the consequences sixty years later: Overcrowded roads, disintegrating infrastructure, and thousands of deaths every year, and a transportation system that makes no sense, mixing long-haul trucking with families in cars, all so that truckloads of stuff can get to the suburban big-box store a little more quickly.
If, however, the introduction of self-driving cars is enough of a disruptive innovation to induce long-run adjustments in the vehicle code and the safety standards for road vehicles, perhaps such abominations as triple trailers and 53 foot containers will be contrary to public convenience and necessity.