Trafikverket & Pilz modernise Swedish rail communications with fibre optics

The Swedish Transport Administration, Trafikverket, has partnered with automation specialist Pilz to modernise safety-critical data communication across the national rail network through the deployment of an optical transmission solution. This engineering project introduces fibre-optic media to upgrade existing relay-based signalling installations within the railway transport sector.

Operational Challenge and Modernisation Needs
Traditional railway communications rely heavily on copper-wire networks to relay safety-critical commands between signal boxes and trackside hardware. Upgrading these installations often presents an operational bottleneck, as fully replacing legacy relay interlockings requires significant capital expenditure and extensive service interruptions. Trafikverket required an engineering approach that would upgrade network throughput and reliability without mandating the removal or fundamental modification of existing safety and control systems. Engineering consultancy Sweco joined Trafikverket and Pilz to solve this systems integration challenge.

Technical Solution and Partner Responsibilities
The partners jointly developed the Safe Relay Messages over Opto (SRO) system. The solution uses Pilz's modular railway control platform, PSSrail, to route and verify vital signalling data over fibre-optic links between signal boxes and trackside field elements.

Under the division of responsibilities, Pilz provided the underlying SIL 4 safety-compliant programmable logic architecture, while Trafikverket specified operational requirements and railway signalling standards. Sweco assisted in systems engineering and integration planning. The system interfaces directly with legacy relay components, digitising and transmitting relay states across optical fibre rather than physical copper lines. This architecture satisfies the safety integrity level SIL 4 standard, ensuring fail-safe transmission parameters, galvanic isolation, and high immunity to electromagnetic interference.

Deployment and Network Implementation
Following field testing on active line sections, the SRO platform received generic approval from Swedish transport authorities. This certification allows Trafikverket to migrate lines from copper to fibre optics incrementally, avoiding individual site-by-site certification procedures. Engineering teams can install the optical communication modules directly alongside operational interlockings, minimising track access requirements and operational downtime during upgrade phases.

Target Applications and Expected Impact
The system targets main-line and regional railway corridors where legacy signalling requires improved data resilience. Concrete use cases include the modernisation of inter-signal box links, level crossing interfaces, and remote trackside asset controls.

Operationally, the transition to optical infrastructure increases signal transmission reliability, mitigates copper theft risks, and improves line availability. The granting of generic type approval lowers engineering and planning expenses for forthcoming rail modernization projects across Sweden, establishing standard interfaces for future digital rail infrastructure initiatives.

Trade Show Presentation
Pilz and Trafikverket will present the operational parameters of the system at InnoTrans 2026, scheduled from 22 to 25 September 2026 in Berlin, Germany.

Edited by Natania Lyngdoh, Induportals editor, assisted by AI.

www.pilz.com