An elevated lineside building housing the levers, switches, and interlocking machinery used to route trains and control signals. In North American practice, this structure is almost universally called an interlocking tower or simply a tower, though the term signal box appears in older literature and imported systems.
Heard on the job
The old mechanical signal box at the junction was torn down last year and replaced with a solid state interlocking.
Related terms
Interlocking tower
A trackside building housing the levers and logic machines that control a local junction.
Lever frame
A mechanical assembly of large handles used to manually operate switches and signals.
Interlocking
An arrangement of signals and switches interconnected to prevent conflicting train movements.