Line 1, shortened to L1, coloured red and often simply called Línia vermella, is the second oldest Barcelona Metro line, after line L3. It is the longest line of the Barcelona Metro, and links L'Hospitalet de Llobregat and Santa Coloma de Gramenet. 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 Iberian gauge tracks, as used by most Spanish main line railways.

Avinguda Carrilet, also known as L'Hospitalet Avinguda Carrilet, is an interchange complex underneath Avinguda Carrilet in the L'Hospitalet de Llobregat municipality, to the south-west of Barcelona, in Catalonia, Spain. It consists of a railway station on the Llobregat–Anoia Line and a Barcelona Metro line 1 (L1) station. The Llobregat–Anoia Line station is served by Barcelona Metro line 8 (L8), Baix Llobregat Metro lines S33, S4 and S8, and commuter rail lines R5, R6, R50 and R60. The services on the Llobregat–Anoia Line are operated by Ferrocarrils de la Generalitat de Catalunya (FGC), whilst the L1 is operated by Transports Metropolitans de Barcelona (TMB).