My first encounter with the Berlin U-bahn (the underground system, as opposed to the S-bahn overground lines) was the strange little U55 shuttle between Hautbahnhof and Brandenburger Tor.
Cavernous halls lead to an enormous two-platform station. One of the two platforms is fenced off and unused.
Into the other trundles a two-car train which shuttles back and forth every few minutes.
It’s very useful, but the station is completely out of proportion with the train.
And it’s the exact opposite of the cramped and crowded Times Square-Grand Central shuttle in Manhattan.
The trains are actually modernised museum-pieces.
It was only when I walked down Unter den Linden, where the central reservation is a building site, that I realised a short but vital underground link is under construction.
By 2019 there will be a service between Hauptbahnhof and the transport hub at Alexanderplatz where the U5 underground line currently terminates: http://www.projekt-u5.de/en.
The 1½-mile link will bring stations to the major tourist spots on Unter den Linden and Schloßplatz, and so take road traffic and some pedestrians out of the crowded tourist area.
Then they’ll no longer have to crane the U55 rolling stock in and out of the tunnel for overhaul like they do on the Waterloo & City Line in London.