cabsignaling

Cab signaling is a railway signaling method in which information about permissible speed and movement authority is transmitted directly to the train’s cab, rather than being conveyed exclusively by trackside signals. The goal is to provide continuous guidance to the driver and, in many implementations, to enforce braking when necessary, enhancing safety and capacity on busy or constrained routes.

A typical cab signaling system comprises trackside equipment that sends data to an onboard cab unit, a driver display or interface, and a safety or control module that interprets the data and sets speed limits, acceleration, and braking commands. The transmission can be conducted via dedicated rail communications, inductive or radio links, and, in modern examples, standardized in-cab systems that integrate with automatic train protection or automatic train operation features. The driver usually sees an indication of the current speed limit, the next required speed, and the available movement authority, with some systems capable of automatically applying brakes to stay within the prescribed profile.

Cab signaling is often used alongside traditional line-side signals, serving to provide continuous guidance in situations where line-of-sight signals are impractical or where higher safety and higher traffic density are required. It is a core component of many advanced signaling architectures, including European systems that use in-cab displays and radio communications, and various national automatic train protection implementations.

Advantages include improved safety through continuous speed supervision, potential increases in line capacity, and better performance in tunnels and dense urban networks. Limitations involve the need for reliable onboard and communications equipment, maintenance requirements, and the complexity of integrating with other signaling and control systems.