The Metropolitan Railway had been extended soon after opening, reaching Hammersmith with the Great Western Railway in 1864 and Richmond over the tracks of the London and South Western Railway (L&SWR) in 1877. The Metropolitan & St John's Wood Railway opened as a single track branch from Baker Street to Swiss Cottage, and this was to become the Met's most important route as it expanded north into the Middlesex countryside, where it stimulated the development of new suburbs. Harrow was reached in 1880, and the line eventually extended as far as in Buckinghamshire, more than from Baker Street and the centre of London. From the end of the 19th century, the railway shared tracks with the Great Central Railway route out of .