Based on Southern Pacific’s common standard plan #1341 circa 1960, the railroad’s nominal car length (coupler to coupler) was 49 feet (1225 feet equaled 25 car lengths).
Mark
Several 1950’s era timetables give siding lengths in 45 ft car lengths (the length of a 40 ft boxcar).
Dave H.
I free-lance HO and my layout is 2 ft wide around the wall. Period is 1962 and a few years prior. (My 1962 HO Police Cruser sets the latest date.) Right now, most cars are 40 foot, but I do have some 50 footers. I would say 2/3 to 3/4 are 40 and the rest 50. Shorter cars allow longer trains for a set siding length.
Since some of my freight cars are very short (6m) and some are quite long (20m) I have standardized on a ‘calength equivalent’ of 8 scale meters (100mm actual,) the typical length between coupler pulling faces of a JNR 4-wheel freight car in 1964.
The longest train my layout can handle is 20 CLE plus 2 locomotives - 2.6 meters. Since one of those locomotives is a pusher picked up at the low end of a visible grade, the longest train that has to fit a staging track is 2.3 meters long (just under 8 feet.)
Shorter trains, locals and interchange units, are restricted to 12 CLE and don’t require pushers. They lay over in staging tracks 5 feet long.
As for the reason for those particular train lengths, I have the best possible reason. Those are the train lengths my prototype was running in 1964.
Chuck (modelting Central Japan in September, 1964)