InterlockingSysteme

Interlocking Systeme are safety-critical railway signaling systems that coordinate signals, routes, and trackside equipment to prevent conflicting movements and protect train operations. The primary function is to ensure that a signal can be cleared only when the intended route is safely set and locked, and that points and other devices cannot be changed or released while a train is on or approaching a conflicting path.

Historically, interlocking began as mechanical systems using lever frames in signal boxes. These evolved into electromechanical arrangements combining relays with mechanical locks, and later into electronic and computer-based interlockings. Modern installations frequently use centralized or distributed computer-based interlockings, which offer higher reliability, easier maintenance, and greater configurability.

A typical interlocking system includes a controller or panel, signal aspects, point (switch) machines, track circuits or axle counters for train presence, and a secure locking and release logic. It interfaces with train detection, power supply, communication networks, and remote monitoring or control centers. The interlocking enforces route locking, interlocking of signals and points, and fail-safe operation to maintain safe rearings and clearances.

Types range from traditional mechanical interlockings to electro-mechanical and electronic interlockings, with modern implementations often described as computer-based interlocking (CBI). Interlockings can be centralized, where a single unit controls multiple locations, or decentralized, distributing control closer to the line elements. In some systems, interlockings are integrated with more extensive signaling architectures, including automatic train control and, in Europe, interoperability standards.

Standards and safety considerations emphasize RAMS, certification, and interoperability. Regulations such as EN 50126-50129-50128 address reliability, availability, maintainability, safety, and safety certification. Cybersecurity and software verification are increasingly important in contemporary deployments.