green representing two or more clear blocks, yellow one clear block and red/lunar white representing a restricting indication, meaning the engineman was permitted to enter his train into an occupied block. The individual marker lamps provide speed information, 12 o'clock being Normal speed, 6 being Medium speed (Limited speed if flashing), 10 being Normal to Medium (Limited if flashing), 2 being Normal to Slow, 8 being Medium to Medium, 4 being Medium to Slow and no lit markers being Slow to Slow. This CPL was first deployed on the Staten Island Railroad (a B&O subsidiary) in the 1920s, and deployed system-wide shortly thereafter. Parts of the Chicago and Alton Railroad received CPLs later, when the B&O gained control of that line. In the 1980s both Amtrak's Chicago Union Station and Metra's Chicago Northwestern Station installed dwarf CPLs to replace earlier signals in those terminals. and as with all U.S. railroads, CSX is slowly replacing all of the remaining CPLs on its system with contemporary vertical color light LED signals. The signals on the old Alton Railroad have also been almost entirely replaced as have many of the CPL dwarfs at the two Chicago terminals. The sole exception is the Staten Island Railroad, which recently upgraded its signaling system with new CPLs using modern Safetran position light equipment. Obsolete mechanical and electrical signals Early mechanical signals The first signals employed on an American railroad were a system of flags used on the Newcastle and Frenchtown Turnpike and Rail Road in the 1830s. The railroad then developed a more effective system consisting of wooden balls, painted red, white or black, and hoisted up or down a pole on a rope-and-pulley system. The initial use of these signals was merely to indicate the on-time status of trains, rather than to control train movements. The wooden balls were often configured with lanterns for nighttime use. Ball signals were first used to direct train movements in 1852, on the New York and New Haven Railroad. Other mechanical signals used during the 19th century include: A disc, painted red and mounted on a revolving pole; it indicated "stop" when positioned to face an approaching train. A pivoted board, called a "smashboard," which could be operated to swing into position across the track. The Reading Railroad used vane signals mounted on wooden towers. Painted boards (vanes) of various colors were moved into position to signify danger (stop),