On tracks that London Underground share with National Rail third-rail stock (the Bakerloo and District lines both have such sections), the centre rail is connected to the running rails, allowing both types of train to operate, at a compromise voltage of 660 V. Underground trains pass from one section to the other at speed; lineside electrical connections and resistances separate the two types of supply. These routes were originally solely electrified on the four-rail system by the LNWR before National Rail trains were rewired to their standard three-rail system to simplify rolling stock use.
బకెర్లూ, డిస్ట్రిక్ట్ లైన్లలో కొన్ని విభాగాలను మూడు రైలు మార్గాలుగా ఎందుకు మార్చారు?
to simplify rolling stock use