Technical Specifications for Interoperability (TSI)
Technical Specifications for Interoperability (TSIs) are the legally binding EU specifications that define the technical and operational requirements every subsystem of the rail system must meet. They are adopted as Commission implementing regulations and take precedence over national technical rules within their scope.
The legal basis for the Technical Specifications for Interoperability is the Interoperability Directive (2016/797), which defines the subsystems of the EU rail system and requires each to be covered by a TSI. Structural subsystems cover infrastructure, energy, trackside and on-board control-command and signalling, and rolling stock. Functional subsystems cover operation and traffic management, maintenance, and telematics applications.
ERA drafts the TSIs on mandate from the European Commission, in working parties with national safety authorities and sector representative bodies. The Commission then adopts them as implementing regulations, giving them direct legal force in every member state.
Before a structural subsystem can be authorised, a Notified Body assesses its conformity with the applicable TSIs and issues an EC certificate of verification; the applicant then draws up the EC declaration of verification on that basis. The TSIs are thereby the yardstick of the entire authorisation chain.
What the TSIs replace
Before TSIs, a subsystem had to satisfy a separate set of national technical rules in every country a train entered. A TSI defines one requirement valid across the EU; national rules survive only for open points and specific cases the TSI does not yet cover.
The practical effect is that a vehicle designed and assessed against the TSIs does not need re-engineering at each border. The CCS TSI is the clearest example: it mandates ETCS as the common train protection system for new and upgraded lines, displacing the national legacy systems.
The 2023 revision and the telematics TSI
The current TSI generation stems from the Digital Rail and Green Freight revision package adopted in August 2023, which updated the CCS, infrastructure, energy, rolling stock, wagon, noise, operation and accessibility TSIs in one coordinated release. The CCS update introduced the specifications known as ETCS Baseline 4.
In February 2026 the Commission adopted a new Telematics Applications TSI, in force from 2 March 2026. It sets common requirements for data sharing, passenger information, ticketing and digital freight services — and designates ERA as system authority for the digitalisation of rail communications.
The revision cycle is continuous: TSIs are reviewed to correct deficiencies, absorb research results and update standard references, so the specifications track the state of the system they govern.