More than 100 years ago, the first kilometers of tunnel in the New York metro network were put into operation. At that time, around 3.5 million people lived in Manhattan and in the other four city boroughs of Bronx, Brooklyn, Staten Island and Queens. In the meantime, New York City alone now has around nine million people living and working there. The population of the metropolitan region today amounts to almost 19 million. Atypically for Americans, the New Yorkers love using their public transport system. A gap in the otherwise extensive network has to be closed on the Far East Side. Line 7, which commences in Queens, is to be extended from Times Square with two parallel tunnels reaching the banks of the Hudson River.
Herrenknecht Double Shield TBMs were used for the first time in the U.S. Two identical machines drove the extension tunnel of Line 7 beneath Manhattan. From Times Square toward the Hudson River and 11th Avenue, the two TBMs bored two 1,400-meter-long tunnels. On their way through slate, granite and serpentine, the machines had to underpass several existing tunnels, including the subway lines beneath 8th Avenue and the three tubes of the Lincoln tunnel. The two Double Shield TBMs achieved breakthrough in June and July 2010.