Automatic and electric light signals was also a first for the railway.
It was worked by steam trains, and despite the creation of numerous vents, was unhealthy and uncomfortable for passengers and operating staff.
Nevertheless, its trains were popular from the start and the Metropolitan Railway and the competing Metropolitan District Railway developed the inner circle around central London (completed in 1884) and an extensive system of suburban branches to the northwest (extending into the adjoining countryside), the west, the southwest and the east (mostly completed by 1904).
Rapid transit first began in London with the opening in 1863 of the Metropolitan Railway,which is now part of the London Underground.
However, smoke from steam engines collected in the tunnels, leading to an uncomfortable passenger experience.
The opening of London's City & South London Railway in 1890 overcame the smoke problem by using electric traction and by the First World War, had led to the development of electric underground railways in Athens, Berlin, Boston, Buenos Aires, Budapest, Glasgow, Hamburg, Liverpool, New York City, Paris, and Philadelphia.