Of the many trends that happened in railroading mid-20th century, one that kind of stuns me is the absolute decline of LCL (less-than-carload) from the end of WWII to 1970 (when it was pretty much gone). Now, I realize that a lot of this was due to the closing of 'small-town' (and not so small town) passenger stations during the 1960s train-offs (some stations were retained for freight service only, but not for that long) as these stations served as feeders and distributors of LCL, but in the large and medium sized urban areas (across the country, not just the North East) railroads had huge LCL freight handling facilities, sometimes with dedicated fast trains between metropoli (famous example: NYC Pacemaker), and in the post-WWII era these facilities were readily adapted the logisitical mechanization improvements gained from that war (e.g. forklift, cart-tractors, mobile powered cranes & winches, pallets, etc - stuff that did exist in the pre-WWII era, but really came into use during it). You can find numbers of company publicity pictures of the workforce at the urban terminals posed in rows with their new freight handling equipment.
Then, 25 years later at the most - bupkis (this happened in the UK by the mid-1970s too, and probably everywhere else) - the dedicate trains long gone, the freight handling equipment moved elsewhere, and the freight stations (eventually) torn down or redeveloped for other uses. Sporadical attempts to revive LCL eventually go nowhere (eg, Amtrak ), and while you could make a case that LCL now goes via piggyback service (or containers), well, not quite the same, is it.
One more thing - remember that some classes of freight have simply vanished, as few (maybe none) towns nowadays have coal dealers, or ice-houses, or stockyards (well, there are stockyards of course, but basically the animals are butchered as close to their feedlots as possible, and the meat, which doesn't need to be feed or watered or exercised as it travels - just refrigerated, is then shipped).