Paul,
Lots of great info there. But based on actual photos and records, and first hand info from my father who working the trucking business his whole life, there were lots of sub 30’ trailers still in use throughout the 50’s, by both railroads and common carriers.
First off, east of the Mississippi, many States had 32’ or 35’ restrictions until 1958.
Second, many carriers prefered 24’ trailers for city delivery, and much more industry was still urban than - no “industrial parks” yet to speak of.
The Southern Pacific used 24’ vans in their capitive service LCL piggy back service well into the mid/late 50’s, if not longer. So did the B&O and others. Jeff Wison’sbook on Intermodal has a 1955 photo of 24’ SP vans on a flat and a 1958 photo of one tractor pulling two 24’ vans.
And, not mentioned yet by anyone, the Delaware, Lackawanna and Western was a big early player - they used 40’ box car frames to build 40’ flats designed for one 32’ trailer - with unique sliding bridge plates rather than hinged ones.
Somewhere I have a very detailed history of the development of piggy back, and it came from an online source, if I can find it, I’ll post a link if possible.
Personally, even though I “know” all this history, I don’t get real hung up about it. I like early piggybacks, I make them look “plausable”, I run them in my 1954 make believe world. I make believe the idiots in Washington got out of the way of piggyback interchange sooner, and I run most every roadname that had early piggybacks on the ATLANTIC CENTRAL.
I have 50’, 40’ and a few 75’ flats with 32’ trailers, a few of those have hitches - just being invented in 1954 - I have lots of 24’ vans on 50’ flat cars - about 80 piggyback flat cars in total.
Roadnames include: ATLANTIC CENTRAL, NH, NKP, PRR, B&O, CN, CP, C&NW, MKT, Reading, UP, NP, Monon, DL&W, Eri