The cards are not primarily an index (the cards themselves contain unique information), but do contain file numbers that refer to three related series: ”Formal Case Files: Bonded Carriers (Truck and Bus), 1927-1933” (case numbers have the prefix BC) (Series 1276); ”Formal Case Files: Auto Transportation Companies, Interstate, 1931-1933” (case numbers have the prefix IS) (Series 1277); and ”Formal Case Files: Motor Vehicle Hauling, 1931-1933” (case numbers have the prefix MVH) (Series 1272).
