With the technical pillar of the Fourth Railway Package, the EU wants to create rapid and lasting harmonisation in international standard-gauge rail traffic. The interoperability standards are to be applied consistently in participating countries. The existing national rules that evolved over time have to be phased out as part of an agreed implementation programme. In an era of rail innovation, the European Union Agency for Railways (ERA) has been tasked with completely modernising European interoperability standards. The ERA continues to operate its One-Stop Shop (OSS) portal for vehicle authorisations and has been issuing cross-border authorisations since June 2019. The ERA works closely with national regulatory authorities in examining applications for authorisation. Switzerland is adopting the technical pillar of the Fourth Railway Package in a series of stages.