London Underground operate nearly 400 route miles of underground railway line, the majority of which is double track. Perhaps surprisingly, less than 50% of this is actually underground, a statistic which owes much to the system's expansion during the 1930's and 1940's when the network expanded into the suburbs over the branch lines of the mainline railway companies. Most of the underground lines are deep level tubes which currently extend for nearly 140 route miles (this will increase when the Jubilee extension comes into use in 1999) with just 32 miles of sub-surface lines built by the original "cut and cover" method.
These pages provide some more interesting facts and figures about the Underground network.

Highest & Lowest
The highest point reached by London Underground trains is at Amersham on the Metropolitan Line at about 500 feet above sea level.  However the highest point above the ground is reached on the Dollis Brook Viaduct on the Mill Hill East branch of the Northern Line which is 60 feet above the road below.
The lowest point on the system is just south of Waterloo station on the Northern, where the tracks are 70 feet below sea level.   The absolute deepest part of the system is also on the Northern where, below Hampstead Heath, the rails are over 220 feet below the ground.
Nearby Hampstead station is also the deepest station on the network at 192 feet below ground level. The platforms here are reached by the deepest lifts on the system which descend 181 feet.

Furthest
The furthest places reached by LU trains are Epping (Central Line) in the North, Morden (Northern Line) in the South, Upminster (District Line) in the East, and Amersham (Metropolitan Line) in the West.

Longest & Shortest
The longest continuous journey on the Underground (without a change of trains) is on the Central Line where a journey from West Ruislip to Epping covers just over 34 miles.   However, the longest journey underground is on the Northern Line: if you catch a train at Morden and travel via the City branch to East Finchley, you will take a continuous journey in tunnel of over 17 miles.
The longest distance between adjacent stations is on the Metropolitan Line; Chesham being nearly 4 miles from its junction with the mainline at Chalfont & Latimer.
The shortest distance between stops is on the Piccadilly Line: Leicester Square and Covent Garden stations being a mere 0.16 miles.  Given the need to use escalators and lifts at each end, it would be quicker to walk!
The shortest line on the system is the Waterloo & City which at 1.38 miles easily beats the former holder of the title, the East London Line (five miles) when the former was taken over from British rail in 1994.

Busiest
The busiest line on the system is the District Line which carries over 180 million passengers per year over its 40 mile length.   However, in terms of passengers per mile, the Victoria is the busiest, carrying about 175 million over its 13.25 mile length each year.
The busiest station on the network is Victoria, closely followed by Oxford Circus, both of which are the start or end points for over 85 million passengers each year.  The next largest is King's Cross with nearly 70 million passengers each year:   given that all three of these stations are on the Victoria line, it is easy to see why this line is the busiest on the network!

UPS and DOWNS
Getting to underground railways usually involves lifts and escalators and the London Underground has a rich variety of both, although lifts are now fewer in number. The escalator (moving stairs) were invented in the 1890s and first one on the Underground was installed by Otis at Earl's Court station in 1911. Such was the success of this form of vertical transport that all new tube stations since the early 20th century were equipped with them. Recently the lift has been making a come back as the requirements of the disabled mean that they are a more suitable means of transport.
The shortest escalator on the system can be found at Chancery Lane station linking the east and westbound platforms of the Central Line which are immediately above each other. The longest escalator is at the new Angel station on the City branch of the Northern Line.
The shallowest lift on the system is at Chalk Farm with a rise of 30 feet, while the deepest is at Hampstead with a vertical rise of of over 181 feet.
There is also one travolator (moving pavement) on the system, which links the Waterloo & City line station at Bank with the main tube station concourse. Just over 300 feet long, it has a gradient of 8 degrees.

Biggest and Smallest
Two stations vie with each other as the biggest on the network, each with 10 platforms - Baker Street and Moorgate.  Baker Street can be argued as the true holder of the title however as all are used by London Underground trains (4 Metropolitan, 2 Circle, 2 Bakerloo and 2 Jubilee) whereas four of Moorgate's are operated by NetworkRail operators (Thameslink 2 and WAGN 2) - the others are 2 Northern and 4 Circle and Metropolitan.
Similarly three stations compete for the title of the smallest station on the network, all having just one platform.  Heathrow Terminal 4 station is unique in being the only tube station with a single platform edge, but the title is probably truly jointly owned by Chesham, one of the Northern outposts of the Metropolitan and Mill Hill East on the Northern. (Single line platforms were also in use on the Ongar branch of the Central and at Aldwych, both of which are now closed.)

Inter-Line Connections
There are a number of connections between the various underground lines to enable stock to be moved around the system and for engineers trains to reach all parts of the system. Some are restricted to certain stock on grounds of size (sub-surface stock is clearly too big for the tube lines) or for technical reasons (e.g. Victoria line). Accordingly, many of the engineers trains can only use parts of the system at night when regular services are suspended
The following provides a guide to these connections:

Shared Tracks (LU)

• Piccadilly and Metropolitan; share the Uxbridge branch from Rayners Lane
• Piccadilly and District; these lines share tracks between Acton Town and Hanger Lane Junction
• Circle Line; shares tracks with the Metropolitan and District
• Hammersmith & City; shares tracks with the District and Metropolitan/Circle

Shared Tracks (with NetworkRail)

• Metropolitan; shares tracks on its northern section from Harrow-on-the-Hill to a point just north of Amersham.
• District; shares tracks with NetworkRail from Gunnersbury on the Richmond branch. In addition, there is a connection at Wimbledon to Wimbledon Park Depot.
• Bakerloo; shares track with NetworkRail north of Queens Park
• Central; there is a single line connection from West Ruislip depot to NetworkRail's High Wycombe line over which all stock deliveries by rail are made to LU.

Open Air Connections

• Ruislip Depot; a siding provides a connection between the depot (and thus the Central line) and the Metropolitan/Piccadilly Uxbridge line
• Ealing Broadway; a link is provided between the Central and District lines
• Barons Court & Hammersmith; links between the Piccadilly and District lines
• Finchley Road to Neasden & Wembly Park; the Metropolitan and Jubilee can use each others tracks under certain conditions between these points, although this is not normal.

Tunnel Connections

• St Marys Curve, Whitchapel; connection between District and East London Line
• Baker Street; connections are provided between the Bakerloo and Jubilee lines
• Kings Cross & Euston Loops; single track links provide a connection between the Piccadilly and Northern lines.
• Finsbury Park; a connection between the Victoria and Piccadilly lines

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