Some of the K-Line by Lionel trucks, on flatcars, were much too small. 1/64? I never measured because I never bought one - obviously way, way too small.
The "Piggyback" box trailers provided with Lionel flatcars recently appear to be right at 1:48 scale - at least in width and height. The photo below shows one of the two from (6-27545) the recetnly released REA PS4 with piggybacks fitted with a Speccast International KB-8 cab. I think it is a good match, if perhaps the tractor is a fraction too small (dare I say, perhaps 4%). The photo below that shows it with a variety of other trucks from 1:43 Peterbilt on the left to a 1:48 Peterbilt and a 1:43 '53 Mack (both converted th "Streets_ and the Speccast tractor with the trailer it is meant to pair with. Lionel offers a tractor for their box van (6-37850 - second image) which I think looks a bit too big for it.
