What is an SPT?

At a glance

A telephone at a signal (or other lineside point) that lets a driver or track worker speak directly to the signaller.

Why: It's a safety-critical communication point, so its position, labelling and product type are all set by standards.

Where: At signals and other lineside points as required by the signalling scheme. Labels must identify the signal and location clearly.

Shown on the copper SLD at the signal, with its circuit back to the exchange or signal box.

Also called: signal post telephone, lineside telephone, signal telephone

Guidance in our words. Read the current issue of each standard before you design to it.