S. Kip Farrington's series of books, Railroading from the Head End, Railroads at War, Railroading from the Rear End, Railroads of Today, Railroads of the Hour, and Railroading the Modern Way make up a continuing period documentary of rail progress from the WWII era through the postwar years. Photographs included are publicity and archive shots from the railroads and news bureaus, as well as builders' photos, all of which I don't recall seeing anywhere else. Some are real gems, like the builders' photos and Santa Fe archive shots of the then-new El Capitan Hi-Level cars -- which were virtually unchanged when I rode them in Amtrak service in 1980.
It's interesting to watch the steam-to-diesel (or, Diesel, as it was properly spelled then!) transition era unfold in what would have been real time as the books were written. CTC was still new at the start of the series, and into its second generation of the technology by the end. Modern steam was still being built when the series started, but by the end, EMD's "GP" series was making a stir. The birth of dome cars on passenger trains, early applications of roller bearings, growth of TOFC intermodal service, and early railroad radio development are all covered as they happened.