Signalling & Interlocking

Railway signalling networks carry life‑critical information. Interlocking systems prevent conflicting train movements, track circuits detect train positions, and control centres manage safe operations – each demanding deterministic, fail‑safe communications with millisecond precision.


Signalling & Interlocking | Overview

Modern railway signalling employs distributed intelligence. Interlocking processors at stations and junctions communicate with trackside equipment, control centres, and adjacent interlockings. This distributed architecture requires networks that deliver deterministic performance – predictable latency, guaranteed delivery, and fault tolerance. Safety certification standards like CENELEC EN 50159 govern these communications, imposing strict requirements on network design, redundancy, and cybersecurity.

Signalling networks operate in harsh railway environments while maintaining continuous operation. Electromagnetic interference from traction systems, vibration from passing trains, temperature extremes, and physical exposure along tracks demand robust hardware and careful installation. Networks must support both legacy signalling protocols and modern IP‑based systems during transition periods, often requiring gateway devices and protocol conversion.

Network Architecture for Safety‑Critical Systems

Signalling networks typically employ ring or dual‑star topologies with redundant paths. Each interlocking connection uses separate physical routes where possible. Time‑sensitive networking (TSN) technologies ensure deterministic delivery of control messages. Network segmentation isolates signalling traffic from other railway systems while maintaining necessary integration points for control centres and maintenance systems. Cybersecurity measures must protect without introducing unacceptable latency or compromising fail‑safe operation principles.


Interlocking Communications – processor‑to‑processor links, control centre connectivity, and adjacent interlocking coordination

Interlocking Communications

Networks between interlocking processors – deterministic links for control coordination, redundant paths for continuous operation, and integration with railway control centres.

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Trackside Signalling Networks – connections to points, signals, track circuits, and level crossing controls

Trackside Signalling

Networks to trackside equipment – connections to signals, points mechanisms, track circuits, axle counters, and level crossing controls with environmental hardening.

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Signalling Control Centre Networks – links to signalling workstations, video walls, and train describer systems

Control Centre Networks

Connectivity to signalling control rooms – workstations, train describers, control panels, and video walls with high availability and deterministic performance.

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Signalling Redundancy & Failover – dual networks, automatic switchover, and continuous operation design

Signalling Redundancy

Fail‑safe network design – dual independent networks, automatic failover mechanisms, and architectures that maintain signalling operation during network faults.

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Signalling Cybersecurity – protecting safety‑critical systems from threats while maintaining performance

Signalling Cybersecurity

Security for signalling networks – protection without compromising determinism, secure segmentation, threat monitoring, and compliance with railway security standards.

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Legacy & Modern Signalling Integration – transitioning between systems while maintaining operations

Legacy & Modern Integration

Network design for signalling transitions – integrating legacy relay‑based systems with modern computer‑based interlockings, protocol conversion, and phased migration strategies.

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Partner Solutions for Signalling Networks

Throughput Technologies partners with manufacturers specialising in railway signalling networking. Westermo industrial switches with EN 50155 compliance provide deterministic networking for interlocking communications in harsh railway environments. ATOP Technologies precision timing switches ensure synchronised operations across distributed signalling systems, meeting millisecond‑level requirements. FlexDSL SHDSL solutions extend network connectivity to remote trackside equipment over existing copper infrastructure. Secomea secure remote access enables signalling engineers to troubleshoot interlocking systems without compromising safety or security. ProSoft Technology protocol gateways facilitate integration between legacy signalling equipment and modern IP‑based networks, while Welotec edge computing devices process data locally at signalling locations.

Future‑Proofing Signalling Networks

Railway signalling evolves toward communications‑based train control (CBTC) and European Train Control System (ETCS) Level 3. Future networks must support moving block signalling with continuous train‑to‑ground communications, predictive maintenance analysing interlocking health data, and integrated traffic management coordinating multiple train operators. Emerging technologies include 5G‑Railway (FRMCS) for next‑generation signalling communications, time‑sensitive networking (TSN) for deterministic control traffic, and cybersecurity measures that protect increasingly connected signalling systems without compromising fail‑safe operation or certification requirements.

Each topic addresses critical components of railway signalling network design, providing guidance for signalling engineers, network designers, and safety managers implementing robust communications for train control systems.