The project involved the underground extension of the current surface metro line which passes through the centre of San Francisco.

The plan for this part of the project was to drill two parallel 2.6-kilometre tunnels for the passage of subway trains, as well as four stations at a cost of $1.6 billion. Of that total, $241 million was awarded to the Italian group Salini Impregilo, its U.S. unit S.A. Healy and partner Barnard C.C.I. Salini Impregilo did the two tunnels, the preliminary work for the future stations, the entry ramp and the extraction well for the tunnel-boring machine (TBM). Apart from the technical difficulties in drilling two tunnels across the centre of a city like San Francisco, another challenge was conducting in a transparent way a dialogue with local residents and taking into consideration the various interests in the area.

Awards: Award of Merit 2015 from Engineering-News Record, an industry publication; The Outstanding Transportation Project 2015 award given by the local section of the American Society of Civil Engineers (ASCE).

Client: City and County San Francisco Municipal Transportation Agency