It is easy to determine if flat bed and van trucks and trailers are 1:48 scale. Normal, run of the mill flat bed or van trucks and semis are 102" wide. Divided by 48 equals 2 and 1/8 inches wide. Thirty or so years ago they were 96" wide for 2 inches. Very few semi trailers (Weaver 53' van trailers being a notable exception) are scale length. the 13 1/4 inch length of the 53' model road trailer uses a lot of room on a train layout. Imagine dedicating a minimum of two feet in front of every dock on your layout for semis to maneuver.
John in Lansing, Illinois