The proposals include a completely new line, Line U5, which will link Bramfeld in the east with the city centre and Osdorfer Born in the west. Two route options are being considered for the western section of the line: a northern alignment running via the University and Lokstedt, and a southern alignment serving Altona Old Town and Ottensen.

"Line U5 must connect the major residential areas with the city centre, while taking into account employment locations, leisure facilities, and future urban development projects," says Elste.

By 2040 the plan also envisages the extension of Line U4 south to Wilhelmsburg and Kirchdorf and east to Horner Geest, and the extension of Line U2 southeast to Lohbrügge.

Horch says that due to public concern over the environmental impact of viaduct construction the city will aim to build new lines underground wherever possible.

A concept study for the expansion of the U-Bahn will be presented to the Hamburg senate later this year, and the city plans to commission a feasibility study during the next legislative period.