Central line (London Underground) and Great Eastern Railway buildings east of , from when the line to Epping was a rural branch line. In terms of total passengers, the Central line is the busiest on the Underground. In 2011/12 over 260 million passenger journeys were recorded on the line. It currently operates the second-most frequent service on the network, with 34 trains per hour (tph) operating for half-an-hour in the westbound direction during the morning peak, and between 27 and 30 tph during the rest of the peak. This makes the Central line the busiest and most intensively-used railway line in the United Kingdom:
London Underground cells". The Waterloo and City Railway opened in 1898, followed by the Central London Railway in 1900, known as the "twopenny tube". These two ran electric trains in circular tunnels having diameters between and , whereas the Great Northern and City Railway, which opened in 1904, was built to take main line trains from Finsbury Park to a Moorgate terminus in the City and had diameter tunnels. While steam locomotives were in use on the Underground there were contrasting health reports. There were many instances of passengers collapsing whilst travelling, due to heat and pollution, leading for calls to clean