"The recent issue of Trains Magazine has a number of articles on the shipment of automobiles via rail but is a bit vague about the timeline for the use of box cars."
The article is not only vague on that timeline, but also fails to mention the use of Evans Auto~Loaders or the NYC Railroad's two designs of auto loaders.
"It has been my understanding -- perhaps misguided -- that automobile shipments after WWII moved from rail to highway over the road trailer and very few cars were shipped in box cars at this time period."
Railroads lost the majority share of new, fully assembled, auto and light truck shipments to trucking in 1932, and never recaptured that advantage until after 1960. Prior to the 1930's, shipments of automobiles and light trucks were dominated by the railroads . In 1932 51.5% of new autos and light trucks were delivered by truck or so-called "drive-aways", the latter two methods of delivery were grouped statistically (during that period), thus it is hard to derive the true percentage hauled by truck. None-the-less, railroads were
"1) is my understanding of the shipment of automobiles via rail correct?"
No, the railroads still handled a good portion of the automobile and light truck traffic during the post war years from which they received a higher profit per ton than virtually any other commodity.
"2) were automobiles being shipped in box cars into the 1950's?"
Yes, by the thousands.
"3) if YES, then what makes were shipped by rail?"
Ford, Lincoln, Mercury, Chevrolet, Pontiac, Buick, Oldsmobile, Cadillac, Chrysler, Dodge, Plymouth, Checker, De Soto, Hudson, Kaiser, Nash, Packard, Studebaker, Willys, and Crosley.
"4) after WWII was box car shipment of automobiles, if shipped in a box car, done using 40-foot or 50-foot box cars?"
40-foot auto cars equipped with Evans Auto~Loaders outnumbered 50-foot auto cars (so equipped) until mid-1957. 40-foot cars were nearly as well suited as their 50-foot companions when small to mid-sized vehicles were shipped. 50-foot cars were purchased in large part to serve the small truck market as well as autos. A good percentage of