Iberian gauge in the context of Interoperability

High-speed railways in Spain have been in operation since 1992 when the first line was opened connecting the cities of Madrid, Córdoba and Seville. Unlike the rest of the Iberian broad gauge network, the Spanish High-speed network mainly uses standard gauge. This permits direct connections to outside Spain through the link to the French network at the Perthus Tunnel. High-speed trains run on a network of high-speed rail track owned and managed by ADIF (Administrador de Infraestructuras Ferroviarias), where the dominant service is AVE while other high speed services such as Avant, Alvia, Avlo, Euromed, Ouigo España and Iryo, as well as mid-speed (InterCity) services also operate.

AVE trains are operated by Renfe, the national passenger high-speed rail operator in Spain, but other companies such as Ouigo España and Iryo compete on the Madrid–Barcelona and other routes in accordance with the European Union legislation. French TGV services run from the border to Barcelona under the TGV inOui brand. Alvia and Euromed trains are also operated by Renfe and have the ability to use both Iberian gauge and standard gauge lines offering high-speed services across the whole Spanish network.

Alvia is a high-speed train service in Spain offered by Renfe Operadora on long-distance routes with a top speed of 250 km/h (160 mph). The trains have the ability to use both Iberian gauge and standard gauge, which allows them to travel on the recently constructed high-speed lines for part of the journey before switching to the "classic" Iberian gauge network to complete it. Trains that run exclusively on high-speed tracks are branded AVE or Avant.

Line 1, often shortened to L1, coloured red and often simply called Línia vermella ("Red Line"), is the second oldest Barcelona Metro line, after Line 3. It is the longest line of the Barcelona Metro and links L'Hospitalet de Llobregat and Santa Coloma de Gramenet, crossing and serving the centre of Barcelona. Originally operated by the independent Ferrocarril Metropolitano Transversal de Barcelona, it is today operated by Transports Metropolitans de Barcelona (TMB) and is part of the ATM fare-integrated main transport system. L1 is the only metro line in Spain to use old Iberian gauge tracks (1674 mm), slightly wider than those used by most Spanish main line railways.

The line was created in 1926 as a means to join the rail stations the city had in the 1920s, and in preparation for the 1929 Universal Exposition. It has been growing since then to become a large line made up of 30 stations, as of 2007, the network's busiest one. These stations are architecturally homogenous, and as in the case of most metro lines in Barcelona, ornamentation is virtually absent from them. Some of them are improving their artificial lighting. Most of the line is underground, except for one short section, and at one point it shares tunnels with mainline tracks.