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.

Railway and metro signaling is entering a new era; one defined by openness, flexibility, and collaboration. In June 2025, Prover launched the Open Signaling Initiative, a dedicated hub for the growing Open Signaling Initiative. The goal is simple: empower infrastructure managers, system integrators, hardware and software suppliers, and safety assessors to work together in reshaping how signaling systems are built, operated, and maintained.

With openness at its core, the initiative drives innovation, enhances long-term sustainability, and gives industry players the flexibility they need to meet future demands.

The need for a more open approach

Today, most signaling systems are delivered as closed, monolithic packages. Many infrastructure managers are seeking solutions based on open signaling principles and standardisation. When existing monolithic systems reach end-of-life, they’re often replaced in one costly leap, a practice that has become the industry norm. The result: high expenses and limited flexibility, slowing down innovation.

Historically, signaling systems were built from off-the-shelf components that any qualified engineer could replace or modify. The Open Signaling Initiative restores that openness while embracing the power of modern, computer-based systems.

Principles of open signaling

Already in use across several projects, the open signaling approach is built on three key principles:

• Open interfaces
  Use of standard communication protocols such as OPC UA, MQTT, and EULYNX/RaSTA, along with data formats like railML, to ensure interoperability.
• Loosely coupled components
  Separation of platform and logic allows individual components to be swapped out without affecting the entire system.
• COTS hardware
  Commercial-off-the-shelf platforms offer cost-efficiency and long-term flexibility.

What does it mean for the railway industry?

With open signaling, infrastructure managers can remain in control. They can reduce risk, modernize systems incrementally, and avoid the disruption and cost of “big bang” replacements.

Systems built on open signaling principles deliver:

• Greater flexibility in procurement
• Easier safety assurance through formal verification
• Long-term sustainability through obsolescence management
• A broader ecosystem of suppliers and integrators

Prover’s role

Prover supports the Open Signaling Initiative through tools and processes grounded in formal methods. Our Signaling Design Automation (SDA) process includes:

• Specification writing using formal logic
• Developing application logic directly from verified specifications
• Platform-independent code generation
• Performing formal verification to support your safety case

Our tools meet CENELEC EN 50716/50128 SIL 4 requirements and have been proven in multiple high-integrity signaling projects.

How do I get involved and get the benefits of the Open Signaling Initiative?

Visit the Open Signaling Initiative to explore how the initiative can benefit your organization. Learn more about the approach, see who’s already contributing, and discover how you can take part.

Whether you’re working to modernize aging relay-based systems or developing next-generation technology, your involvement matters. Join us in making signaling more open, collaborative, and future-ready.

Let’s build a more open future together

The Open Signaling Initiative offers a clear roadmap for gradual, controlled change. It’s about creating a signaling ecosystem that’s modular, flexible, and built to evolve – much like modern IT systems. This shift gives infrastructure managers and technology providers greater freedom of choice, encourages innovation, and supports long-term sustainability.

A more open future isn’t just a vision, it’s already in motion.

Discover how you can contribute at www.opensignaling.org.

Prover contributing in ForTeS project in Germany for DZSF with DLR

The EULYNX consortium and the Europe’s Rail System Pillar are publishing the specification of the latest generation of interlockings called “digital interlockings”. This is a precise description of interfaces of the interlocking core with its adjacent systems and of the behavior of several adjacent systems, for example, of the point controller. An important goal is to empower infrastructure managers through the standardized modularization of the interlockings to buy subsystems from different suppliers.

EULYNX is a European initiative that standardizes railway signaling interfaces. It enables interoperability between systems, reduces vendor lock-in, and supports modular, digital, and cost-efficient signaling solutions.

Objectives and goals of the project

While many suppliers develop and offer corresponding products, it remains difficult for infrastructure managers to use subsystems of different suppliers as part of the same interlocking. After all, the interoperability of the subsystems and the safe function of the interlocking composed thereof need to be proven – a task for which the supplier of the complete interlocking used to be responsible in the past. Proof and approval of combinations of subsystems from arbitrary suppliers poses a new challenge.

The ForTeS project aims to demonstrate an efficient and reliable approval process for modular systems. This involves two main steps:

1. The first step is about proving that the specification implies the necessary (interoperability, safety) properties. There, the project relies on the extremely rigorous method of formal verification.
2. The second step is about proving conformity of a system implementation to the specification. There, the project relies on highly automated tests as an efficient and broadly applicable method; the certification test cases published by the EULYNX consortium serve as a basis.

Together, these steps will be demonstrated through a simulated approval of a point controller. The resulting assessment report, alongside the formal proof and test suite, will be a key project outcome, helping to accelerate the safe and cost-effective rollout of digital interlockings.

Prover’s contributions

With decades of experience, Prover’s contribution focuses on applying formal methods in railway signaling to ensure compliance with regulatory requirements. Prover will leverage its extensive industry expertise to identify potential applications of formal methods, align them with European railway standards, and reinforce their impact on approval processes. Prover will also evaluate the feasibility and objectives of using formal methods in EULYNX systems, comparing alternative scenarios if applicable.

By contributing to the development of robust and standardized approval methods using Formal Methods, Prover supports the wider adoption of digital interlockings and supports the shift toward more modular, vendor-independent railway systems. This work is closely aligned with our Open Signaling initiative, which promotes openness, transparency, and efficiency in railway signaling to drive innovation and reduce lifecycle costs.

Timeline and project contractors

Project start: May 2025
Duration: 24 months
Main contractor: Prover Technology AB
Subcontractors: Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) and ESE Engineering und Software-Entwicklung GmbH

Read the original press release from DZSF (in German):

https://www.dzsf.bund.de/SharedDocs/Standardartikel/DZSF/Projekte/Projekt_205_DSTW-Zulassungsprozesse.html