"I take it trouble started Post WW2?"
Well, it all starts back around 1820 when a guy named MacAdam, a Scot, invented a way to make sturdy roads with fine gravel and tar (also know as Asphalt)...
And then, a guy named Ford came up with an assembly line to make lower cost cars and trucks...
And then lots of folks owning brand new lower cost cars and trucks (with encouragement from Henry) wanted "paved roads"...
An aside, did you know that the whole Charcoal grill industry was started by Henry Ford, he had lots of tiny bits of hardwood left over from constructing the bodies of the early cars, and he wanted folks to drive around a lot and have picnics with hot food (cooked on a charcoal grill) to sell more cars. Basically he was a tightwad that hated to throw away waste wood when he could still sell it and "make a buck". Kingsford Charcoal is actually a company started by old Henry and later "spun-off" from Ford Motor company (true fact).
And then the government started started paving dirt roads with asphalt (roads in rural areas around WNY were mostly dirt until the late 20's)...
And then there was a little event called the Great Depression....
In between the assembly line and the Great Depression was a World War, the government took over the railroads and ran the wheels off of everything...
Then there was the Roaring Twenties when the RRs where going great guns and built things like Buffalo Central Terminal (it was built with foundations and drainage pipes to support the future addition of 2 more platforms / 4 more tracks)...
And then there was another World War (My Pop flew a P-51 escorting Bombers into occupied Europe) which ran the wheels off all the railroad equipment all over again...
Then the RR folks invested in lots of new passenger cars (re-equipped 20th Century limited of 1948, etc.) but the GI's coming back to the "homefront" after years riding in stinky crowded troop trains fell in love with travelling in their own car when and where they wanted to....
The End....
Ok, just one edit, somewhere along the way some Wright guys invented the airplane an a Brit invented the Jet Engine... That forever doomed long distance passenger trains to "too slow" status...