Atlas Trainman HO 20006254 1937 AAR Box Car Kit, Southern Pacific #115818Atlas Trainman HO 20006254 1937 AAR Box Car Kit, Southern Pacific #115818 Part Number: 843069180463 Description Atlas Trainman HO 20006254 1937 AAR Box Car Kit, Southern Pacific #115818 The 1937 AAR Box Car is widely recognized as the first standard freight car design to be voluntarily adopted by the majority of railroads throughout the United States. Although previous USRA designs also achieved widespread distribution, their success was mostly due to