for the lines were proposed. One serious plan was to close the line between Marylebone and South Ruislip/Harrow-on-the-Hill, and convert Marylebone into a coach station. Metropolitan line trains would be extended to Aylesbury and BR services from Aylesbury would be routed to London Paddington via High Wycombe. Also the line north of Princes Risborough would close. However, this did not happen as Baker Street and London Paddington would not have been able to cope with the extra trains and passengers. What did happen was total route modernisation. This was an ambitious plan to bring the lines into the modern era of rail travel. Class 115s were replaced by new Class 165s. Semaphore signals were replaced by standard colour light signals and ATP was fitted on the line and trains. Speed limits were increased to 75 mph (only 75 due to running on London Underground track between Harrow and Amersham), all remaining fast loops at stations were removed and the line between and Aynho Junction was singled. Stations were refurbished and even reconstructed (£10 million spent on stations alone), and signal boxes and the freight depots/sidings were demolished. Regular services to Banbury, and a few specials to Birmingham were introduced and a new maintenance depot was built at Aylesbury. This was a massive undertaking and work began in 1988 and by 1992, the route had been completely modernised, demand for the service had grown considerably and the route had become profitable. Since modernisation the route has seen further improvements (see Chiltern Main Line). Electrification was considered but was deemed to be too expensive as the Thames Line sector would then have to be electrified as well. Another reason electrification did not take place was that some part of the line ran on underground lines, which were electrified as 4-rail 660 V DC, while British Rail preferred 25 kV AC overhead traction for lines north of London. Success of the modernisation implemented by NSE has made it possible for the Chiltern Main Line to compete with the West Coast Main Line between London and Birmingham, and there are now plans to increase speeds and quadruple sections of the line, returning the line to the state it was before the Beeching Axe. New trains Network SouthEast started a programme of replacing old rolling stock up to privatisation. Chiltern 165 Great Eastern 321 Great Northern 365 Island Line 483 (ex London Underground 1938 Stock)