Operating Era: 1901-1961. Great Northern. Between 1901 and 1917 GN built over 20,000 40' DS truss rod box cars. During their lives the cars were upgraded, rebuilt, renumbered and repainted numerous times. Beginning in 1925 all cars except one series delivered with steel center sills were rebuilt with add-on steel center sills and steel needle beams, raising the cars 10" above their previous height. While truss rod cars were outlawed in interchange in 1952, cars with steel center sills were exempted, allowing them to run much longer. Beginning in 1911 cars were built with safety appliances. With the general renumbering of 1915 the oldest cars were rebuilt with safety appliances, a process that would have been completed by about 1923. Cars from 1911 on used tapered sill steps attached to the bottom of the side; earlier cars used straight steps attached to the side of the side. Doors of 1911 had an additional stiffener near the top. Beginning in 1921 cars shopped for improvements would have received the 72" herald and three-color paint job. All roadworthy cars were modernized in a program that began in 1925 and lasted at least to 1931.