, released by
Annett's key The lever frame is located in the signal box, which can be a building at ground level or a tower, separated from or connected to an existing station building. Early lever frames were also built as
ground frames next to the track, without any form of shelter and were usually operated by traincrew and not permanently staffed. Especially in England, lever frames with the pivot underneath the floor of the signal box were common. This design's relatively short lever angle is a major disadvantage, as it requires more force to move the lever. Therefore, later, especially in Germany, lever frames with pivots inside the signaller's room were used, that allow for a lever angle of approximately 180°. By the movement of individual levers (or sometimes cranks), signals, points, track locks,
level crossing gates or barriers and sometimes navigable
movable bridges over waterways are operated via wires and rods. The signaller chooses the correct combination of points,
facing point locks and signals to operate, which will control the movement of each train through their area of control. The lever frame contains
interlocking designed to ensure that the levers cannot be operated to create a conflicting train movement. Each interlocking installation is individual and unique to the location controlled. The interlocking may be achieved mechanically or by electric lever locks, or (more usually) a combination of both. == Variants ==