From closed systems to open standards

Across the railway industry, many infrastructure managers are still operating relay-based signaling systems. They work – but maintaining them is costly, spare parts are disappearing, and the expertise required to service them is becoming harder to find. At the same time, demands for higher capacity, improved safety, and faster modernization are growing. Increasing train traffic, automation initiatives, and stricter safety standards are accelerating this transformation.

To move forward, the industry needs to shift from proprietary, vendor-specific systems to open and standardized architectures. This is the foundation of open signaling – which promotes interoperability and vendor independence for the next generation of railway signaling systems. At the heart of this transformation lies COTS – Commercial Off-The-Shelf components.

What COTS means for railway signaling

COTS refers to standard, industrial components – such as PLCs or I/O systems – that are already available on the market. The term originates from the software industry and refers to ready-made, industrial solutions that can be integrated with minimal customization. Unlike proprietary hardware developed for a single supplier’s platform, COTS enables signaling systems to be built on open, accessible technology.

For the railway sector, this brings several advantages:

• Flexibility: Hardware can be replaced or upgraded without redesigning the entire system.
• Vendor independence: Infrastructure managers are no longer locked into one supplier.
• Cost efficiency: Using standard components reduces lifecycle and procurement costs.
• Scalability: Systems can be deployed and adapted more easily across networks.

But more importantly, COTS is not just about cost or convenience – it’s what makes open signaling technically and commercially possible.

Prover’s role – safety through formal methods

Using COTS in signaling introduces new opportunities, but also new challenges. Especially when it comes to how safety is demonstrated. If signaling hardware becomes open and interchangeable, and the signaling principles are moved to software, then much of the safety validation must move to software too.

Experience from modernization projects shows that using digital twins is an effective way to manage this transition. Digital twins allow infrastructure managers to test, validate, and verify the principles behind new COTS-based systems before deployment – ensuring full safety integrity throughout the process. Prover’s use of formal methods, i.e., mathematical proof-based verification, ensures that safety-critical software behaves exactly as intended, regardless of the underlying hardware platform.

With this approach, operators can safely adopt COTS-based systems while maintaining the same rigorous safety assurance as in traditional, proprietary systems.

Migration: from relay to open architecture

For many infrastructure managers, the journey starts with migration. Moving from aging relay-based systems to COTS-based platforms is often the first practical step toward open signaling.

A concrete example is the Stockholm Metro modernization, where Prover and partner Cactus introduced COTS-based PLCs while retaining existing relay interlockings. Using a five-step migration process supported by digital twins, the project achieved a smooth transition to a modernized architecture – reusing proven logic and ensuring safety through formal verification. This approach reduces risk, ensures continuity, and creates a future-proof foundation for digital evolution. Read more about Relay Signaling Migration here.

Open signaling – a shared vision for the industry

Open signaling is not a product; it’s a concept and a way of thinking. By combining open interfaces, standardized hardware (COTS), and formally verified software, the railway industry can build signaling systems that are:

• Software-driven, through verified logic
• More efficient, through shared standards
• More sustainable, through reduced lifecycle complexity

Prover’s contribution to open signaling is to make this vision practical – transforming safety-critical verification into a digital, automated process that supports an open and innovation-driven railway ecosystem. Read about the Open Signaling Initiative here.

Shaping the future of railway signaling

COTS is more than a hardware choice, it’s a catalyst for change in railway signaling modernization. It enables the shift from closed, proprietary systems to open, future-proof architectures where flexibility, safety, and innovation coexist. Together with open signaling principles, COTS paves the way for a modern and future-ready railway infrastructure. And with Prover’s expertise in safety verification and signaling software, the industry can move forward with confidence – building signaling systems that are open, interoperable, and safe by design.