Through the U4 subway line, HafenCity was connected to the rail-based local transportation system to downtown Hamburg back in 2012. The route, which is about 4 km long, runs at depths between 20 and 40 metres beneath the road or water surface and under existing and planned buildings. The route was completed in three construction stages. The first involved the connecting structures at the existing Jungfernstieg station in the heart of Hamburg. From there, two tunnels with a diameter of about 5.6 metres and a length of about 2.8 km each were constructed using shield tunnelling through to the new Überseequartier subway station. The two new stations on the U4 line, Überseequartier and HafenCity Universität, as well as the 1.2 km tunnel track in between, were then made in the third stage using cut-and-cover construction method.