arms and counterweights Cab signaling equipment Automatic train control Automatic train protection Automatic train stop Wayside signaling equipment DC code systems Electronic communication systems Electronic interlocking Relays Railway signals Switch machines Track circuits Central Control signaling equipment Computer-based manual Control systems Computer-based traffic management systems Dark territory control systems Electro-mechanical centralized traffic control machines Note US&S was the only company to make 180 degree electronic bells. See also General Railway Signal – The other major US railway signaling company North American railroad signals Safetran – Another US railway signaling company, now part of Siemens References External links 1881 establishments in Pennsylvania American companies established in 1881 American subsidiaries of foreign companies Manufacturing companies based in Pittsburgh Manufacturing companies established in 1881 Railway signalling manufacturers