Berlin’s U-Bahn underground train network has launched a 4G LTE service spanning all nine lines, comprising 155.64 km of track and 175 stations, and plans to roll out 5G soon. Until now, like many subway systems built over a long period (dating back to 1902 in Berlin’s case), the U-Bahn has had a patchwork of wireless technologies, comprising inconsistent WiFi, 4G, and even areas of 5G access. As in most other such projects, the Berlin mobile network is based on a neutral host model with access provided by all three major operators, O2 Telefonica, Vodafone Germany and Deutsche Telekom. Telefonica took the lead role in partnership with Berliner Verkehrsbetriebe (BVG), the public transport company managing Berlin’s subway. One novel feature…