Railway train signal practise

This is a description of an automatic block signal system used on single track. Signals are located over or to right of track governed. Cab signals are a development of recent years. Indications must be easy to read. Three colors are used — red, yellow, and green. Signals are dependent upon track circuits for proper control and operation. Energy for operation is supplied by storage batteries trickle charged from commercial sources of alternating current. Current for lamps is taken directly from a-c. lines with automatic cut over to storage batteries in case of failure of supply line. Lens unit of light signal is a doublet combination with a special lens for use on curves. Absolute permissive block system provides head-on protection from station to station and permits following movements with clear signals with intermediate blocks between stations. Tonnage markers permit heavy trains to pass red signals on grades where, if stopped, these trains could not be started. Signal circuits are designed on the closed circuit principle. An organization for construction and maintenance of a Signal Department is outlined.