four times: The lines S8 and S9 cross the river via the Steinheimer Mainbrücke, between the stations Hanau Hauptbahnhof and Steinheim. The City-Tunnel Frankfurt drives under the Main between the stations Ostendstraße and Lokalbahnhof / Mühlberg, the branch is located approximately under the southern riverbank, this tunnel uses all lines except the S7. The Alte Niederräder Brücke uses the S7 between Frankfurt Central Station and Niederrad. The lines S8 and S9 cross the Main via the immediately adjacent Neue Niederräder bridge, also between Frankfurt main station and Niederrad. Via the railway bridge Hochheim the line S9 between the stations Mainz-Bischofsheim and Mainz-Kastel takes the "shortcut" from the Frankfurt airport to Wiesbaden. The Nidda is crossed in three places, namely once each of the lines S1 to S6. The Line S6 runs part way next to the Nidda, but crosses it only once: Between the stations Bad Vilbel and Bad Vilbel Süd, drive from the line S6, the bridge of the Homburg railway between Frankfurt west station and Rödelheim, drive from the lines S3-S5, and the younger of the two railway bridges in Frankfurt-Nied, namely those of the Main-Lahn-Bahn, traveled by the lines S1 and S2. The fourth major river in the region, the Kinzig, currently has no contact with the S-Bahn network. This will only change with the construction of the North-Main S-Bahn line to Hanau, as the existing **Frankfurt-Hanau line crosses the Kinzig just north of the Hanau West station on a bridge from 1926. Tunnels S-Bahn in Frankfurt has several tunnels: Through the City-Tunnel Frankfurt all S-Bahn trains except the S7. Also not in the tunnel are the short-distance trains of the S1 and the S8 that stop at Frankfurt's main station, as well as the S9 coming from Wiesbaden during the low load period. After crossing the river Main, the tunnel branches off to Frankfurt-Süd station and in the direction of Offenbach am Main. It has seven underground stations and is about long. In the Main Guard Konstablerwache section, there are two more outer subway tracks. At the station Konstablerwache can be changed in the direction of travel at the same platform in the subway U6 and U7. As the only railway tunnel, it undercuts the Main next to the subway line A. A branch to the planned northern line to Hanau is prepared. In 2010, the modernization of train control increased capacity by 2 trains per