From my research 75' piggyback flats came into general use in 1955, and 86' in 1959. So how long did the 75's stay on until they faded away?
According to Vol. 1 of "The TTX Story" by James D. Panza, Richard W. Dawson and Ronald P. Sellberg, ISBN 978-0-9993584-0-5, one of the first 75 foot piggyback cars was a General Motors design, built by their Electro-Motive Division. This car possessed a conventional height centersill the length of the car with a deck that dropped down between the trucks giving it an appearance similar to a depressed center flatcar. It was not successful.
The successful Pennsylvania Railroad F-39, 75 foot piggyback car began to arrive in 1955 and was intsrumental in the formation of Trailer Train. The PRR/TTX F-39 remained in trailer service until 1984. Any F-39s in service after 1984 were used as regular flatcars, with their end ramps and hitches removed. These cars met their end rather quickly, in light of the number of much newer 89 footers made surplus by the shift to container wells vs. flatcars.
restorator From my research 75' piggyback flats came into general use in 1955, and 86' in 1959. So how long did the 75's stay on until they faded away?
There is some good information here:
https://www.model160.com/n-scale-news-blog/intermodal-flat-cars-the-85-pioneers/
They note that the first 85' flat cars were introduced in 1958 by P-S and in 1959 by ACF.
TTX also has a nice timeline here:
https://www.ttx.com/about/our-history/
They also note that 85' piggy back flatcars were introduced in 1958.
I would imagine after 40' trailers became standard in the 1960's, the 75' flat cars would have fallen out of TOFC use pretty quickly and repurposed not being able to carry 2 40' trailers.
The 85' flat cars seemed to linger for a few years after 45' trailers became the standard around 1982, being able to carry 1 45 and 1 40' trailer. On the M160 site, there is a photo of a yellow TT painted F85A 85' flat car with a single 45' trailer in 1986, but probably uncommon by then.
Rio Grande. The Action Road - Focus 1977-1983
There still would have been a role for 75' flatcars to play because even though they were not heavy duty flatcars by any means, there were still dimensional loads that were long enough to need an idler car even with a regular 60' flat car, sometimes an idler car at both ends.
One challenge is tracing the cars is that once they were no longer TOFC it might be that TTX released them to its member railroads.
Just out of curiosity I got out two of my Official Railway Equipment Registers from eras when even the 85' cars were more or less obsolete. The first ORER is July 1975 and I looked under TTX. It shows a surprising number of 75' flats, with ATTX (so no hitches) reporting marks, AAR designatio F39, F 39a through c. I didn't tally up how many but certainly a few hundred. About seventy 75 footers had JTTX reporting marks (cars specially modified by railroads for specific loads). Even more interestingly given the late date, a few hundred 75 footers also still had TTX reporting marks meaning they had hitches and bridge plates - genuine TOFC equipped. Presumably some shippers were OK with that.
So two decades in, TTX's own fleet of 75 footers was clearly reduced but there were still somewhere around 400 to 500 of them on the roster, with about half still equipped for trailers. And again perhaps TTX at some point sold off 75 footers to other railroads and such.
So now we move to the 1994 ORER (I don't own any ORERs between 1975 and 1994). Now we are about 40 years in for the 75 footers so normal car retirement would be setting in. I again looked under TTX. It shows about 30 75 footers with ATTX reporting marks AAR designation FM or FMS. Five 75 footers with JTTX reporting marks. None with TTX and indeed only two 85 footers under TTX.
Having said all this, the TTX entries are huge and long and in tiny print and it might be that some 75 footers escaped me in both searches. But clearly the 89 footers ruled the day in 1994 - page after page after page.
I have to say these numbers for the 75 footers surprised me a bit -- and pleasantly surprised since now I feel much better running my Walthers 75 footers on my circa 1967-1969 layout.
Dave Nelson