Significant investment has been made in building road and rail links between regions in Denmark, most notably the Great Belt Fixed Link, which connects Zealand and Funen. It is now possible to drive from Frederikshavn in northern Jutland to Copenhagen on eastern Zealand without leaving the motorway. The main railway operator is DSB for passenger services and DB Cargo for freight trains. The railway tracks are maintained by Banedanmark. The North Sea and the Baltic Sea are intertwined by various, international ferry links. Construction of the Fehmarn Belt Fixed Link, connecting Denmark and Germany with a second link, will start in 2015. Copenhagen has a rapid transit system, the Copenhagen Metro, and an extensive electrified suburban railway network, the S-train. In the four largest cities – Copenhagen, Aarhus, Odense, Aalborg – light rail systems are planned to be in operation around 2020.