remarkably short time. As many as a dozen clerks might work in a single RPO car, although fewer would be required if part of the car was used for transport of previously sorted mail or (often in a separate compartment) express and baggage. Railway mail clerks were subjected to stringent training and ongoing testing of details regarding their handling of the mail. On a given RPO route, each clerk was expected to know not only the post offices and rail junctions along the route, but also specific local delivery details within each of the larger cities served by the route. Periodic testing demanded both accuracy and speed in sorting mail, and a clerk scoring only 96% accuracy would likely receive a warning from the Railway Mail Service division superintendent. Interurban and Streetcar systems were also known to operate RPOs. The Boston Elevated Railway car being noted as making circuits of the city to pick up mail. In the United States, RPO cars (also known as mail cars or postal cars) were equipped and staffed to handle most back-end postal processing functions. First class mail, magazines and newspapers were all sorted, cancelled when necessary, and dispatched to post offices in towns along the route. Registered mail was also handled, and the foreman in charge was required to carry a regulation pistol while on duty to discourage theft of the mail. Standardization Because of the physical and mental demands placed on RPO clerks, the Railway Mail Service pushed the adoption of standardized floor plans and fixtures for all RPO cars, with the first plans published in 1885. The RMS also pressed for improved lighting fixtures to help the clerks see the addresses on the mail they sorted, first by improving the reflectors in the 1880s, then calling for discontinuance of oil lamps in the 1890s and the first experiments with electric lighting in 1912. Clerks' safety was also of great concern to the RMS, with the first comprehensive statistics on work-related injuries published in 1877. Through the second half of the 19th century, most RPO cars were painted in a somewhat uniform color scheme regardless of the railroad that owned or operated them. Most were painted white with trim in either buff, red or blue, which made the cars stand out from the other cars. By the 1890s, this practice had waned as railroads painted their RPO cars to match the rest