Standards Compliance in Tenders: Managing TSI, CENELEC and DIN EN

Introduction

Anyone opening a technical specification in the rail industry for the first time encounters abbreviations such as TSI LOC&PAS, EN 50126, DIN EN 45545-2, or ISO 22163 on almost every page. These standards references are not decorative: they define the technical and regulatory guardrails within which a vehicle can be authorised. A bid that overlooks even one critical standards requirement risks, at best, costly rework and, at worst, exclusion from the tender procedure.

According to the UNIFE World Rail Market Study 2024, the European rolling-stock market is worth EUR 63.3 billion, with annual growth of 7.3% in Western Europe. In this market, manufacturers compete on price, technology, and their ability to work through complex standards landscapes completely and without error. Those who fail lose the contract or risk years of delay in vehicle authorisation.

The standards landscape in the rail industry has few parallels. Unlike automotive engineering, where a small number of central frameworks (such as UNECE regulations) set the boundaries, rolling-stock construction combines European interoperability directives, harmonised EN standards, national special rules, and sector-specific quality standards. The DIN Railway Standards Committee (FSF) represents German interests in the European and international standardisation bodies CEN/TC 256 and ISO/TC 269. A search for “rail” in the ISO database alone returns more than 880 results.

This article provides a structured overview of the most important standards groups, explains their relevance for bid managers, and uses concrete examples to show where typical pitfalls lie. For the wider context, see the complete process from technical specification to functional specification.

An overview of the standards landscape

The standards referenced in a rolling-stock technical specification can be divided into four broad groups. Each has its own origin, validity, and consequences of non-compliance. A typical technical specification for a regional rail vehicle refers, directly and indirectly, to a three-digit number of standards.

TSI: the European interoperability layer

No new vehicle can operate in the EU without the Technical Specifications for Interoperability (TSIs). They are developed by the European Union Agency for Railways (ERA) and, since the Fourth Railway Package (adopted in April 2016 and fully applicable since June 2019), have been the central instrument for vehicle authorisation in the EU. Every TSI is directly applicable EU law.

The following TSIs are particularly relevant to rolling stock:

• TSI LOC&PAS: Locomotives and passenger rolling stock. By far the most extensive TSI for vehicle manufacturers, it sets requirements for structure, traction, braking, doors, passenger information, and much more. ERA provides its own LOC&PAS application guide.
• TSI SRT: Safety in railway tunnels: fire protection, evacuation, emergency lighting.
• TSI PRM: Accessibility for persons with reduced mobility: boarding aids, spaces, information systems.
• TSI NOI: Noise emissions: limits for pass-by noise, stationary noise, and interior sound levels.
• TSI CCS: Control-command and signalling: ETCS and ERTMS compatibility. According to ERTMS statistics, 15% of core-network corridors are currently equipped with ETCS, with the aim of equipping the whole core TEN-T network by 2030.

The 2023 TSI revision: what changed

In March 2023, the Railway Interoperability and Safety Committee adopted the comprehensive 2023 TSI revision package. It entered into force on 28 September 2023. The revision has a direct effect on bid work because it introduces transitional provisions with two phases: a design phase and a production phase with no time limit. TSI conformity is demonstrated at the end of the design phase.

This means that technical specifications created before September 2023 may refer to the old TSI version. Bids submitted in 2025 or 2026 must clarify whether the old or new version applies and which transitional provisions take effect. This cannot be settled at a desk; it requires coordination with the contracting authority.

CENELEC EN 5012x: functional safety

The EN 50126 / EN 50128 / EN 50129 series (often collectively called EN 5012x) governs the safety of all electronic and software-based systems in rolling stock. The series is based on IEC 61508 but tailored to rail. Its core is the Safety Integrity Levels (SIL): four levels define how reliably a safety-related system must operate and therefore directly determine the engineering and evidence effort.

EN 50716: the new software standard

On 30 October 2023, CENELEC adopted EN 50716:2023. It replaces the former EN 50128 (signalling software) and EN 50657 (rolling-stock software) with one unified standard. According to QA Systems, EN 50716 will completely replace EN 50128 by 2026.

The main changes are:

• Agile development: EN 50716 permits iterative development models (Agile, Scrum) through phase-based validation. This departs from EN 50128’s rigid waterfall model.
• AI and machine learning: The standard includes explicit rules for AI/ML components in safety-related software, a first for CENELEC railway standards.
• Cybersecurity: Integration with CENELEC TS 50701 for cybersecurity requirements not yet provided for in EN 50128.
• Formal methods for lower SILs: EN 50716 extends requirements for formal proof methods to SIL 1 and SIL 2, where they were previously compulsory only at higher SIL levels.

EN 50126’s V-model structures the entire development process: on the left (descending) side, requirements are progressively refined from system definition through risk analysis to detailed design. On the right (ascending) side, those requirements are systematically demonstrated through tests and validation. Every stage on the left has a corresponding verification stage on the right.

In practical terms, if a technical specification requires a particular SIL for a subsystem, that directly affects engineering effort, evidence documents, and bid cost. A SIL 4 system requires far more verification than a SIL 1 system. Costs rise significantly with each SIL level, because more extensive testing, formal methods, and independent assessment are required. This distinction must be represented correctly in the bid.

Harmonised EN standards: the technical detail

In addition to TSIs and CENELEC safety standards, technical specifications cite dozens of harmonised European standards for specific technical areas. The DIN FSF standards committee coordinates their development and national implementation as DIN EN standards. Their scope ranges from the fire behaviour of interior cladding to the electromagnetic compatibility of power electronics.

Some of the standards groups most frequently referenced in technical specifications are:

Relative frequency of references in typical regional-rail technical specifications (qualitative assessment based on industry experience, not a quantitative survey).

EN 45545: fire protection as the leading standard

Hardly any technical specification can do without EN 45545. The series comprises seven parts and was last substantially updated in 2024: EN 45545-3:2024 (fire resistance of fire barriers) and EN 45545-4:2024 (fire-safety requirements for rolling-stock design) were published in March 2024.

EN 45545-2 (requirements for materials and components) defines three hazard levels: HL1 (lowest risk), HL2, and HL3 (highest risk, for example tunnel vehicles). Each component is assigned to a material group and must meet the test criteria for the relevant hazard level. In practice, this means the same interior lining may have different approval requirements depending on its operational profile (interurban service versus a metro with long tunnel sections).

Each of these standards also has its own editions, parts, and national annexes. The Wissmann company’s 2019 overview of DIN standards in rolling-stock construction illustrates how broad the spectrum is even for a single supplier. For a vehicle manufacturer responsible for the overall system, the effort multiplies.

ISO 22163 (IRIS): quality management for the rail industry

While TSIs and EN standards place technical requirements on the product, ISO 22163:2023 addresses the manufacturer’s management system. As a sector-specific extension of ISO 9001, it sets additional requirements for rail, including:

• Project management: with specific requirements for planning, monitoring, and risk management beyond ISO 9001.
• Configuration management: combined with change management since the 2023 revision. Particularly relevant to traceability of requirements throughout the product lifecycle.
• Design and development: requiring complete traceability from customer requirements through design evidence (requirements traceability).
• Obsolescence management: critical for vehicles with 30+ year lives that contain electronic components with far shorter availability cycles.

IRIS Certification Rev. 04 has applied to certification audits since 1 April 2024. Existing Rev. 03 certifications can be transitioned to Rev. 04 from April 2024. DQS describes Rev. 04 as leaner and more efficient in the certification process. DNV also highlights the new sustainability requirements.

National special rules: the often underestimated factor

Despite European harmonisation, national technical rules continue to apply alongside TSIs in many EU Member States. These “notified national technical rules” (NNTRs) often cover areas not, or not fully, covered by TSIs. ERA manages them through the Single Rules Database (SRD), which replaced the older NOTIF-IT platform in November 2020.

An example shows how active this area is: Austria alone notified thirty-three national rules in the SRD in May and June 2024. After review, ERA concluded that parts of them were not consistent with the EU legal framework. National regulation and European harmonisation pull in different directions, and this remains an ongoing issue for bid work.

In Germany, the Federal Railway Authority (EBA) publishes the applicable national rules and provides its own Railway Vehicles Manual as guidance for manufacturing and authorisation. An important step forward was the joint declaration of intent by VDB, EBA, BMDV, VDV, and DB AG, signed on 30 January 2025, to make the approval process more efficient. The memorandum particularly concerns applying NNTRs in the authorisation process for railway vehicles, including module testing.

Even where a technical specification refers primarily to TSIs, the national rules of the country of operation must also be checked. For cross-border vehicles, such as an EMU for service between Germany and Switzerland, the national requirements of both countries may apply. The first Stadler FLIRT with ETCS GUARDIA for three-country operation shows how complex certification for multi-country vehicles becomes in practice.

Typical practical challenges

Knowing the standards is one thing. Working through them correctly in the bid process is another. The same problems recur in practice.

1. Sheer volume

A typical technical specification for a regional rail vehicle refers, directly and indirectly, to a three-digit number of standards. TSI LOC&PAS alone internally refers to dozens of further EN standards. Each must be checked for relevance, the correct version identified, and its compliance status assessed. At an OEM such as Alstom, which according to its own supplier page works with more than 21,000 suppliers in 83 countries, this task multiplies across the entire supply chain.

2. Cross-references and standards chains

Standards refer to other standards. EN 45545-2 (fire protection) refers to test methods in EN 45545-1, which in turn refers to ISO test standards. One requirement in a technical specification can therefore trigger a chain of five or more documents, all of which must be checked. The problem is exacerbated when standards in the chain have different publication dates, a constellation regularly encountered with the 2023 TSI revision and the simultaneously updated EN 45545 parts.

3. Version conflicts

Years often pass between preparing a technical specification, submitting a bid, and authorising the vehicle. According to a European Parliament study (2023), Germany typically sees seven to eight years from competitive call to series production. Standards are updated during that time. Whether the version referenced in the specification or the version valid at the time of authorisation prevails regularly becomes contentious.

4. Room for interpretation

Many standards deliberately formulate requirements abstractly. What “appropriate measures to minimise fire risk” specifically means depends on the subsystem, operational profile, and interpretation of the notified assessor (Notified Body). Two experts may reach different assessments, which does not make expert routing in the bid process any easier.

5. Documentation errors with long-term consequences

A current example shows what happens when standards compliance is not tracked accurately in documentation: for Stadler FLIRT trains in Norway, outdated documentation led to damage to 16 EMUs. Newly delivered Stadler BEMU trains in Schleswig-Holstein also experienced software problems that affected vehicle availability. Standards compliance does not end with bid submission; it has an effect throughout the vehicle lifecycle.

Standards compliance in the bid process

Standards checking is not an isolated work step; it runs through the entire path from technical specification to functional specification. At its core, it means systematically answering four questions for every standards-related requirement:

The VDB requirements management guide recommends electronic exchange in ReqIF (Requirements Interchange Format) for this allocation, so standards links remain consistent across tool boundaries. In practice, however, ReqIF is not yet used everywhere; many technical-specification processes still rely on Excel and Word. The EuroSpec standard for requirements management defines six core areas, including traceability and validation/verification, which are directly relevant to standards compliance.

Tools for standards compliance

Today there is a broad range of tools for managing standards references during bid preparation, from manual spreadsheets to integrated requirements-management systems.

Since 2025, Siemens has integrated AI capabilities in Polarion that can automatically analyse incoming tender documents and extract requirements. IBM DOORS is also used for requirements tracking in major rail projects, such as Melbourne’s AUD 11 billion Metro Tunnel Project, where thousands of requirements were coordinated across several contractors. In addition, specialised tools such as Dassault Systèmes’ Reqtify offer a traceability overlay with more than 100 interfaces.

Ultimately, the specific tool matters less than the discipline: every standards reference must be identified, versioned, assessed, and assigned to an owner, whether this happens in an Excel spreadsheet or an ALM system. We describe where Excel reaches its limits in this task in Excel vs. platform.

AI and standards compliance

Automatically recognising standards references in unstructured documents, comparing them with current editions, and resolving standards chains: this is where AI systems can genuinely help. Prover Technology identifies three main problems with specifications in the tender phase: incomplete, inconsistent, and incorrect. AI support can mitigate all three.

Typical use cases:

• Extraction: automatically recognise standards identifiers (for example, “EN 45545-2:2020” or “DIN EN 50155:2017”) in free-text requirements, even where spelling is inconsistent or references are abbreviated.
• Version checking: compare the edition referenced in the technical specification with the currently valid edition. Especially relevant after the 2023 TSI revision and the 2024 EN 45545 updates.
• Cross-reference analysis: identify indirectly referenced standards (standard A refers to standard B, which is not explicitly named in the technical specification). Here, AI can automatically resolve the complete standards chain.
• Reuse: suggest compliance assessments from earlier projects when the same standard is referenced in a comparable context. According to Bidara, the cross-industry content-reuse rate is 66%, a potential that is particularly high in standards compliance.
• Classification support: suggest an initial assessment (OK/OKB/NOK) based on the standards reference and internal knowledge base, which the subject-matter expert reviews and approves. Read more in our article on AI in the bid process.

Conclusion

TSIs (revised in September 2023), CENELEC safety standards (with the new EN 50716), harmonised EN standards (EN 45545-3/4 updated in March 2024), ISO 22163 (IRIS Rev. 04 since April 2024), and national special rules (still active despite harmonisation): the rail industry’s standards landscape is not getting simpler. Without structured processes and suitable tools, this web is difficult to manage.

But it can be managed: with a well-maintained standards matrix; with platforms such as Tendric; with structured expert routing; and with AI-supported extraction and version checking. Those who handle standards compliance rigorously do not only win the next contract; they also save themselves years of authorisation rework.