The European railway signalling landscape changed significantly in 2023. The new Technical Specification for Interoperability — Control Command and Signalling (TSI CCS 2023) is not just a regulatory update. It redefines how ETCS systems are designed, integrated, and certified across Europe for the next decade.

Whether you are a signalling engineer working on an ETCS deployment or a project manager planning a fleet upgrade, understanding TSI CCS 2023 is now essential. This is the first article in a three-part series. We cover the context behind the update and the six key technical changes you need to know.

Why TSI CCS 2023 Was Necessary

The 2016 TSI CCS framework had a fundamental problem: fragmented amendments created inconsistent ETCS implementations across different countries and projects. Infrastructure managers were dealing with multiple parallel baselines, unclear national deviations, and no structured cybersecurity requirements.

TSI CCS 2023 solves this by consolidating everything into a single, unified architecture. The objectives are clear:

• Reduce national deviations and supplier dependency
• Enable modular, future-proof system architectures
• Align ETCS with modern safety and cybersecurity standards
• Prepare European railways for 5G-based communication and automated train operation

Annex A is now the single authoritative source for all mandatory ETCS specifications — replacing the patchwork of previous amendments.

The Six Key Changes

1. ETCS Baseline 4 System Version 2.1

Baseline 4 SV2.1 is the technical backbone of TSI CCS 2023. It consolidates prior releases, stabilises interfaces for long-term deployment, and brings meaningful functional enhancements:

• Improved positioning and odometry accuracy
• Refined braking curve calculations
• Full ATO (Automatic Train Operation) integration support
• Multi-bearer communication capabilities
• Revised interface specifications that reduce complexity across ETCS components

2. Cold Movement Detection (CMD) — Now Mandatory

CMD prevents unintended train movements during standstill by continuously monitoring motion data from onboard sensors. Under TSI CCS 2023 this is no longer optional.

CMD can be implemented integrated within the ETCS OBU software or as a standalone module, validated according to EN 50129 and EN 50657. For retrofit projects on older fleets lacking redundant tachometers or digital brake sensors, additional hardware will be required — plan for this early.

3. Train Interface Module (TIM) Standardisation

TIM standardises the boundary between ETCS and TCMS (Train Control and Management System), enabling modular integration across different fleet types. It integrates with odometry, brake systems, the DMI, and RBC, and supports advanced ATO operations.

Implementation methods include physical sensors such as continuity loops, pneumatic checks, on-board estimation algorithms, and driver declarations under strictly defined conditions.

4. Ethernet Consist Network (ETH-CN)

ETH-CN replaces legacy communication buses such as MVB and CAN, delivering high-bandwidth, deterministic communication across the train. Key features include VLAN-based traffic segregation, built-in redundancy, and full electromagnetic compatibility compliance.

Hybrid architectures — ETH-CN alongside legacy buses — are permitted during the transition period, allowing projects to migrate incrementally rather than all at once.

5. Mandatory Cybersecurity Under EN 50701

This is a genuinely new requirement with no equivalent in TSI CCS 2016. EN 50701 mandates a full cybersecurity lifecycle embedded into the system development process. Security levels range from SL1 to SL4:

• ETCS kernels must achieve SL3
• Radio Block Centres (RBCs) must achieve SL4

Compliance requires cryptographic protections, access controls, event logging, and formal patch management processes.

6. FRMCS Migration Path

TSI CCS 2023 defines a structured three-phase migration from GSM-R to FRMCS (Future Railway Mobile Communication System), based on 3GPP 5G NR technology:

• Phase 1 (from 2025): Dual-Bearer — GSM-R and FRMCS operate in parallel
• Phase 2: Hybrid operation
• Phase 3 (post-2035): FRMCS-Only

FRMCS brings higher bandwidth, lower latency, and enhanced cybersecurity compared to GSM-R.

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