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Genorma lists the EN 50126-2:2017 base document and a separate EN 50126-2:2017/A1:2024 amendment. Confirm that your order covers the document set required by the project, rather than buying an amendment without the underlying text. Genorma base record; A1:2024 record.
Buy the correct Part 2 document set
BSI's railway series listing also identifies the combined national designation BS EN 50126-2:2017+A1:2024 as current. Match the designation and amendment treatment to your procurement specification; a separate amendment, a combined edition and a tracked-changes product should not be assumed to be the same purchase. BSI series and product information.
What the systems approach adds
Part 2 addresses safety within the RAMS life cycle using a technology-independent system approach. The published scope includes risk assessment, derivation of system safety requirements and allocation of safety integrity requirements to subsystems. It covers signalling, rolling stock and fixed installations. Importantly, its scope restricts SIL derivation to safety-related electronic functions: it is not a basis for assigning a SIL to every non-electronic function. Genorma scope.
A useful buyer question is therefore “what safety claim are we purchasing evidence for?” rather than “what SIL is this whole product?” Asking only for a headline label can hide assumptions about installation, interfaces and operation. Request an explanation of the claimed function and the system in which it is intended to work, then have the responsible engineering team assess the applicable requirements.
How Part 2 differs from the related standards
| Document | Purchasing focus | Useful question for the supplier |
|---|---|---|
| EN 50126-1 | RAMS life-cycle process. | How is the project organising its RAMS objectives and evidence? |
| EN 50126-2 | System approach to safety. | How do identified system hazards connect to requirements and responsibilities? |
| EN 50129 | Safety-related electronic signalling systems. | What supports the signalling system's functional-safety claims? |
| EN 50716 | Railway software development. | Which software, tools and application data are included in the development evidence? |
These are selection questions, not a prescribed compliance checklist. The railway standards family overview provides the wider context.
Five records to request before selecting a supplier
For a system-level purchase, a short evidence request can reveal whether competing quotations describe the same task. The following practical request list is an original buyer aid.
- A boundary drawing. Ask which interfaces, operating modes and external dependencies the proposed work includes. Mark what remains the operator's or another supplier's responsibility.
- A hazard-to-requirement map. Ask how the supplier will connect identified hazards to the requirements it is responsible for meeting, and how changes to those requirements will be communicated.
- An allocation statement. Identify which functions are implemented electronically and which protections depend on people, procedures or other technologies. Avoid using a single integrity label as a substitute for that distinction.
- An evidence and review plan. Name the expected deliverables, their owners and the planned review points. Ask what information must arrive from other parties before a conclusion can be reached.
- A document and assumption register. Record the agreed standard editions and the operating assumptions that limit the supplier's claims.
The aim is to compare the completeness of the proposals before comparing price. A quote that excludes interface analysis may describe substantially less work than a quote that includes it, even if both mention EN 50126-2.
Example: a new signalling interface on an existing route
Imagine a project adding an interface between an existing signalling installation and a new monitoring or control subsystem. The purchasing team initially asks each bidder to provide an “EN 50126-2 compliant interface”. That phrase leaves several questions unanswered: what information crosses the boundary, which failure conditions matter, who detects them and what actions depend on the interface?
A better brief describes the intended operating modes and asks the bidders to state their assumptions and exclusions. It also names the team that will assess system-level effects outside the supplier's equipment. The resulting comparison can distinguish equipment documentation from analysis of the integrated function. This example is a procurement scenario, not a finding that any particular architecture is safe.
The public scope does not provide project-specific RAMS targets, product certification rules or a safety-authority approval process. It also distinguishes changes to accepted systems from their unmodified portions. Those boundaries make the agreed project scope and acceptance arrangements important purchasing inputs. BSI scope and exclusions.
Edition and buying questions
Is the 2007 Part 2 document the same standard?
No. BSI records the 2017 standard as superseding the withdrawn PD CLC/TR 50126-2:2007 technical report, with a changed scope. Do not select the older report merely because its number resembles the current standard. BSI history.
Do I also need Part 1?
Review both scopes against your role. Part 1 addresses the wider RAMS process; Part 2 concentrates on the system approach to safety. A project responsible for both needs to plan access accordingly.
Does A1:2024 change the application scope?
Genorma's amendment record says the scope remains the same as EN 50126-2:2017. That does not mean every provision is unchanged; read the licensed amendment to understand its detailed changes. Amendment scope statement.
Sources and edition check
- Genorma: EN 50126-2:2017.
- Genorma: EN 50126-2:2017/A1:2024.
- BSI: scope, earlier report and series editions.
Catalogue records and purchase links checked on 7 October 2026. Examples and evidence requests are original buying guidance, not an engineering assessment or a replacement for the standard.