In the late 1990s, Barcelona's metropolitan railway network was made up exclusively of lines connecting peripheral areas with the center of the city. The L9 project was planned to avoid this centrality and directly connect the densely populated peripheral districts and the various local, regional and high-speed railway lines. The project was later divided into Lines 9 and 10, with a common trunk but different branches to cover more territory.

When completed, Metro L9 will be the longest Metro line in Europe with a length of 30 miles. The line will include 52 stations, 20 of which will be exchanges connecting with local railways, high speed trains, tramways and other Metro lines. L9 will link strategic points throughout the Barcelona region including the airport, ports district, Trade Fair, medical and educational facilities and popular tourist areas.

The automatic train equipment and power systems use the latest technology in urban transport systems and serve as a model for other new underground systems around the world. transitworks' parent company (GPO) has performed complete construction management services on various project components including stations, tunnels, viaducts and related systems.