Faced with an ever-aging fleet of cars and growing traffic levels after WWII, the American railroads embarked on an ambitious car building program. The Postwar AAR boxcar design that developed became one of the most important freight car designs ever. Featuring a 10-6 interior height and in both forty foot and fifty foot lengths, the majority of boxcars built between 1945 and 1960 were based on this design. Although standard designs, over the years these cars were built with various ends, roofs and doors.