London–Aylesbury line

Class 165 and 168 trains at London Marylebone

From Marylebone the line runs through a series of tunnels as far as Finchley Road, from where the line runs overground and runs parallel to the Metropolitan and Jubilee lines. At Neasden Junction, the Chiltern Main Line diverges to the west, while the Aylesbury line continues north parallel to the underground lines. The line then joins the Metropolitan line tracks a few yards south of Harrow-on-the-Hill station and shares this track with the London Underground's fast Metropolitan line services to Amersham from Baker Street. Beyond Moor Park, the line to Watford diverges.

Harrow-on-the-Hill station

Between Rickmansworth and Chorleywood, the M25 motorway crosses on a viaduct. After Chalfont & Latimer station, the Chesham branch diverges, and the main line continues to Amersham, the terminus for Metropolitan line trains. Beyond Amersham, the line returns to Network Rail control and runs northwest to Aylesbury, following the A413 road. The Princes Risborough line joins the main line at Aylesbury, where Chiltern Railways have a maintenance depot. There, the line becomes single track, and after Aylesbury Vale Parkway, freight only, passing through Quainton Road to Calvert, the site of a major waste transfer station and landfill site. Beyond Calvert, at the former junction, the line turns east to join the Varsity Line, while the trackbed of the former Great Central Main Line continues northwest.

Aylesbury station

London Underground own the track and co-run on the line between Harrow on the Hill and the property boundary north of Amersham.[3]

The line serves the following stations:

• London Marylebone
• Harrow on the Hill
• Rickmansworth
• Chorleywood
• Chalfont and Latimer
• Amersham
• Great Missenden
• Wendover
• Stoke Mandeville
• Aylesbury
• Aylesbury Vale Parkway
• (Quainton Road)

Passenger services are provided by Chiltern Railways. From Marylebone to Neasden Junction the track is shared with the Chiltern Main Line and from Harrow to Amersham the track is shared with London Underground's Metropolitan line, and is used by their "fast" services. As a result, all Chiltern trains must be fitted with the tripcock braking system to run on Underground lines. Marylebone Signalling Control Centre controls all the signals on the line between Marylebone and south of Harrow, and also from north of Amersham to Aylesbury. Marylebone can see all train movements throughout the line but does not control the signals on the Metropolitan line section. These are operated by London Underground signal cabins at Harrow, Rickmansworth and Amersham. The Network Rail-controlled section of the line is fully equipped with ATP, one of three lines in Britain to have this (the others being the Chiltern Main Line and the Great Western Main Line). As a result, all Chiltern trains must be equipped with ATP equipment.

The line operates lower frequency timetables during autumn as trains need to take more time to brake due to the leaves that fall on the line in the heavily wooded section between Amersham and Rickmansworth.[4]

• Following completion of a major track work project in December 2006, journey times on the line were cut by about 10 minutes. Major track replacement work is under way on the London Underground parts of the line, to increase maximum speeds and reduce delays.[8]
• The line north of Aylesbury was reopened to regular passenger traffic in 2008 as far as the new Aylesbury Vale Parkway station.[9] In the long term, the line is to reopen beyond Aylesbury Vale Parkway to allow passenger services to reach Milton Keynes Central and Bedford via East West Rail.[10][11][12]
• A proposal announced in March 2010 would route the future high speed line, High Speed 2, parallel with a section of the Chiltern Main Line. If this is undertaken, it will be a non-stop service, with no interconnections with the Chiltern Line.[13]

These are the passenger usage statistics on the National Rail network from the year beginning April 2002 to the year beginning April 2012. Large increases in the final year in some stations are mainly due to the introduction of Oyster Cards on the National Rail Network. The reason there were no usage figures in the first three years for stations from Amersham to Harrow-on-the-Hill was because these figures were not yet separated from the London Underground figures, who own and share the same tracks at this point. Aylesbury Vale Parkway has no previous data for the first five years as it only opened in 2008.[14]

• Foxell, Clive (2010). The Metropolitan Line. History Press. ISBN 978-0-7524-5396-5.
• Horne, Mike (2003). The Metropolitan Line, an Illustrated History. Capital Transport. ISBN 978-1-85414-275-7.