long stretch of which runs along the existing mainline. Through Hammerbrook the trains run on a concrete viaduct and in a tunnel under the centre of Harburg. The line was extended in 1984 along the Niederelbebahn to Neugraben. The line to Bergedorf was placed on separate tracks due to increased traffic on the main line during the 1990s as a result of German reunification. For the same reason, S-Bahn service between Bergedorf and Aumühle was suspended in 1994. The section to Reinbek was reopened in 1997; completion to Aumühle was delayed until 2002 due to court challenges from local residents. In 1999, Allermöhe station (between Mittlerer Landweg and Nettelnburg) opened in the new housing development of Neuallermöhe-West. Since December 2007, the S3 has served stations between Neugraben and Stade. The groundbreaking for a long line from Ohlsdorf to the airport took place in 1991, and again in 2001; the line was opened on 11 December 2008 and has been fully operational since 12 December 2008. Northbound S1 trains split at Ohlsdorf, the front section to the airport, the rear section continues to Poppenbüttel. Operating company The S-Bahn is operated by S-Bahn Hamburg GmbH, a subsidiary of Deutsche Bahn AG. The company is answerable to DB Regio Nord and was formed in 1997. The S-Bahn is represented in German cities with a logo consisting of a white "S" in a green circle. In Hamburg the same logo with a red background was used for a few years before November 2007. The company currently employs approximately 1200 personnel in the driving, maintenance, train departure and resource management divisions. Another 300 employees are responsible for security and cleaning, through subsidiaries. Lines The network covers about , and serves 68 stations. It consists of two trunk routes crossing the city in an east-west direction – the northern Hamburg-Altona link line and the southern City S-Bahn – and six connecting routes (two in the western part of the city and four in the eastern part). The trunk routes connect at Altona and Hauptbahnhof. are separated from other rail services, are shared with regional and cargo traffic. About is in tunnel, are single track. There are four main lines (S1, S21, S3, S31) and two additional lines during peak hours (S11, S2). Lines with single-digit numbers use the "City-S-Bahn" via Jungfernstieg, with two-digit numbers the Verbindungsbahn via Dammtor. Until 2002, some Regionalbahn services were given S-Bahn