Login or register (free and only takes a few minutes) to participate in this question.
You will also have access to many other tools and opportunities designed for those who have language-related jobs (or are passionate about them). Participation is free and the site has a strict confidentiality policy.
Explanation: These are situated at places, such as Port Bou, where trains cross from a standard gauge network (eg the SNCF) to a network with a different gauge (eg Renfe). The operation is carried out automatically. Trains consisting of Talgo-type rolling-stock, such as the overnight Paris Austerlitz - Madrid Chamartín sleeper (used to be called the 'Puerta del Sol') are able to change fairly quickly from one gauge to another. Similar installations are found between the Russian system and Eastern European systems (e.g. Brest-Litovsk).