M25 motorway

M25
London Orbital Motorway
M25 motorway   A282 Dartford Crossing Show interactive map Shown with the UK motorway network Show UK motorways map
Junction 13 looking south
Route information
Part of E15 and E30[1]
Maintained by Connect Plus (contracted to National Highways)
Length	117 mi (188 km)
Existed	1975–present
History	Opened: 1975 Completed: 1986
Major junctions
Orbital around London (in conjunction with the A282)
Anti-clockwise end	Dartford (Dartford Crossing southern approach)
Major intersections	J3 → M20 motorway J5 → M26 motorway J7 → M23 motorway J12 → M3 motorway J15 → M4 motorway J16 → M40 motorway J21 → M1 motorway J23 → A1(M) motorway J27 → M11 motorway
Clockwise end	Thurrock (Dartford Crossing northern approach)
Location
Country	United Kingdom
Counties	Kent, Surrey, Berkshire, Greater London, Buckinghamshire, Hertfordshire, Essex
Primary destinations	London Dartford Crossing Sevenoaks Gatwick Airport Heathrow Airport Watford Stansted Airport Brentwood
Road network
Roads in the United Kingdom Motorways A and B road zones
← M23 → M26

The M25 or London Orbital Motorway is a major road encircling most of Greater London. The 117-mile (188-kilometre) motorway is one of the most important roads in the UK and one of the busiest. Margaret Thatcher opened the final section in 1986, making the M25 the longest ring road in Europe upon opening.^[a] The Dartford Crossing completes the orbital route but is not classed as motorway; it is classed as a trunk road and designated as the A282. In some cases, including notable legal contexts such as the Communications Act 2003, the M25 is used as a de facto alternative boundary for Greater London.

In the 1944 Greater London Plan, Patrick Abercrombie proposed an orbital motorway around London. This evolved into the London Ringways project in the early 1960s, and by 1966, planning had started on two projects, Ringway 3 to the north and Ringway 4 to the south. By the time the first sections opened in 1975, it was decided the ringways would be combined into a single orbital motorway. The M25 was one of the first motorway projects to consider environmental concerns and almost 40 public inquiries took place. The road was built as planned despite some protests that included the section over the North Downs and around Epping Forest which required an extension of the Bell Common Tunnel.

Although the M25 was popular during construction, it quickly became apparent that there was insufficient traffic capacity. Because of the public inquiries, several junctions merely served local roads where office and retail developments were built, attracting even more traffic onto the M25 than it was designed for. The congestion has led to traffic management schemes that include variable speed limit and smart motorway. Since opening, the M25 has been progressively widened, particularly near Heathrow Airport.

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