Differences between Verifier and Validator according to EN50126, EN50128, and EN50129

Railway systems demand uncompromising safety and reliability. Standards such as EN50126, EN50128, and EN50129 have long provided a structured framework for achieving high levels of safety through rigorous processes. Among these processes, verification and validation play pivotal roles. Although they may seem similar, each has a distinct focus and purpose. This blog entry explores the differences between a verifier and a validator in the context of these European standards, highlighting their roles, responsibilities, and how they contribute to a safe railway environment.

Overview of the Relevant Standards

EN50126 – RAMS

EN50126 provides guidelines for the specification and demonstration of Reliability, Availability, Maintainability, and Safety (RAMS) in railway applications. It establishes a life-cycle approach for safety management, ensuring that safety is integrated from the design phase through to decommissioning. Within this framework, both verification and validation are essential to confirm that the system meets its prescribed safety targets.

EN50128 – Software for Railway Control and Signalling

Focusing on the software aspects of railway control and signalling systems, EN50128 emphasizes the importance of stringent development processes. Verification and validation in this standard ensure that the software is built in accordance with the specified requirements and operates reliably under real-world conditions.

EN50129 – Safety-Related Electronic Systems for Signalling

EN50129 covers the safety aspects of electronic systems used in railway signalling. It outlines the methods for demonstrating that safety-related systems comply with necessary safety integrity levels (SILs). Both verification and validation processes help establish that the systems are both correctly designed and function safely during operation.

Understanding Verification and Validation

A common phrase in systems engineering is:

• Verification: “Are we building the system right?”
• Validation: “Are we building the right system?”

Verification

Verification is the process of checking that the outputs of a phase meet the predefined inputs and requirements. It is performed throughout the development cycle and typically involves activities such as reviews, inspections, and testing. In the context of railway systems, verification ensures that each component—whether it be software, hardware, or integrated systems—conforms to its specifications as detailed in the relevant standards.

Validation

Validation, on the other hand, focuses on the overall system and its ability to fulfill its intended operational purpose. It is generally performed towards the end of the development process or during system acceptance testing. Validation examines whether the final product meets the user’s needs and operates correctly within its intended environment. For railways, this means confirming that the system not only meets technical specifications but also performs safely and effectively in real-world scenarios.

The Roles: Verifier vs. Validator

The Verifier

A verifier is an individual or team responsible for ensuring that each stage of the development process adheres to the established process and technical requirements. In practice, the verifier:

• Conducts regular reviews, inspections, and tests throughout the system’s development.
• Focuses on technical compliance, ensuring that the system is built according to the planned process.
• Works closely with the development team to identify discrepancies early on.
• Often operates within the same organization that is developing the system, although independent verification is sometimes employed for critical components.

The Validator

The validator is tasked with confirming that the final product meets the end-user’s requirements and performs safely under actual operating conditions. Key responsibilities of the validator include:

• Assessing the overall system functionality and performance.
• Ensuring that the system is fit for its intended purpose, not just in theory but in practice.
• Conducting tests under realistic operational scenarios to simulate real-world conditions.
• Typically, the validator is an independent party, providing an unbiased review of the system’s effectiveness and safety.

Key Differences Highlighted by the Standards

While both roles are integral to the safety life cycle, EN50126, EN50128, and EN50129 outline clear distinctions:

• Focus and Timing:
  • Verification is an ongoing process throughout the system’s development, emphasizing conformance to technical specifications and design documents.
  • Validation occurs later, verifying that the completed system meets operational and user requirements in its intended environment.
• Scope of Evaluation:
  • Verifiers concentrate on component-level details, ensuring that each part of the system performs as specified.
  • Validators take a holistic approach, evaluating the integrated system’s performance and ensuring that it delivers the intended safety outcomes.
• Independence:
  • While verifiers can be part of the development team, there is a strong recommendation in safety-critical industries for independent verification to avoid conflicts of interest.
  • Validators are generally independent of the development process, offering a fresh perspective to ensure unbiased assessment of system functionality and safety.
• Regulatory and Safety Implications:
  • Compliance with verification requirements is essential to meet the detailed technical criteria laid out in the standards.
  • Successful validation is critical for the final certification and acceptance of the railway system, directly influencing its operational approval and safety integrity.

Best Practices for Effective Verification and Validation

Adhering to EN50126, EN50128, and EN50129 involves a disciplined approach:

1. Early Integration:
   Begin both verification and validation processes early in the project lifecycle. Early reviews and iterative testing can prevent costly rework later.
2. Clear Documentation:
   Maintain thorough documentation of requirements, design decisions, and test results. Traceability is crucial for both verifying and validating safety claims.
3. Independent Reviews:
   Engage independent verifiers and validators to provide objective insights and ensure unbiased assessments of the system.
4. Continuous Improvement:
   Use feedback from both verification and validation activities to refine the system and address potential safety risks before deployment.

Conclusion

In the realm of railway safety, the roles of verifier and validator are distinct yet complementary. Verification focuses on ensuring that the system is built according to design specifications, while validation confirms that the final product meets operational needs and user expectations. Together, these processes form the backbone of safety assurance in accordance with EN50126, EN50128, and EN50129, ensuring that railway systems operate safely, reliably, and efficiently.

Understanding and correctly implementing both verification and validation is critical—not just for compliance with international standards, but for safeguarding lives and maintaining public trust in railway systems.

To learn more about railway safety and engineering, explore our RAMS training courses at https://ramsrail.com/rams-courses/.