The U4 is a line of the Hamburg U-Bahn, which opened in 2012, serving 12 stations. It is the shortest line of the network, with a length of 11.9 kilometres (7.39 mi) and from Jungfernstieg to Billstedt it shares tracks with the U2. From Wikipedia
Replacement buses extend U3 travel times by up to 20 minutes, while U2 now offers uninterrupted service after two years of construction.
