ETCS System Requirements Specification (Subset-026 + companion subsets)

Scope

Subset-026 is the ETCS System Requirements Specification, the core document defining the functional behaviour, modes, braking curves and air-gap language of the European Train Control System at Baseline 4 Release 1 (v4.0.0). Published by ERA as part of the CCS TSI Appendix A mandatory specifications, it is the primary reference for suppliers developing onboard and trackside CCS subsystems and for notified bodies and project engineers assessing ERTMS/ETCS implementations.

SUBSET-026, the ETCS System Requirements Specification, is the core document defining the functional behaviour of the European Train Control System, covering the operating modes a train can be in, the braking curve calculations that determine permitted speed profiles, and the standardised data language exchanged between trackside and on-board equipment (commonly referred to as the ETCS 'air-gap' language). It is published as part of the Baseline 4 Release 1 specification set, the current mandatory ETCS baseline referenced in Appendix A of the CCS TSI, and is typically issued together with a set of companion subset specifications covering interfaces, safety requirements and test specifications that together make up a complete ETCS baseline. As the primary functional reference for the whole ETCS system, it is used by suppliers developing both on-board and trackside control-command subsystems, and by notified bodies and project engineers assessing whether a given ETCS implementation correctly follows the specified functional behaviour. Its version -- Baseline 4 Release 1, version 4.0.0 -- is the mandatory specification currently referenced by the CCS TSI, with no newer baseline yet listed as an ERA-confirmed mandatory replacement. Suppliers building interoperable ETCS equipment must implement the functional behaviour it defines precisely, since ETCS interoperability depends on all suppliers implementing the same specified behaviour rather than each developing an independent interpretation.