SNCF COMPUTER-CONTROLLED SIGNAL BOXES

SNCF computer-controlled signal boxes are provided with two stages, the first being the control unit and the second the locking unit. The control unit is derived from the route programmer; it selects the routes automatically, sets them up and provides protection for worksites on the track. The locking unit verifies and locks the routes. The authors stress more particularly the reasons that have led to computers being introduced into signalling systems, first for auxiliary functions and then progressively for all functions. They explain how the computer-controlled signal box fits into the whole range of modular systems adopted by the SNCF.