The M25 motorway, or London Orbital, is a 117-mile (188 km) circular motorway around Greater London, United Kingdom. It was built during the 1970s but was only completed in 1986. It is one of the busiest roads in Britain due to its proximity to the capital city. Since there is no motorway running through the city, it is the quickest way of travelling between the north and south and east and west of London. It also connects the four main London airports, Heathrow, Gatwick, Stansted and Luton.

The motorway passes through five counties, Kent, Surrey, Buckinghamshire, Hertfordshire and Essex. It also crosses the River Thames at the border of Essex and Kent. Known as the Dartford Crossing, vehicles either use the Queen Elizabeth II Bridge when travelling in a clockwise direction or the Dartford Tunnel when travelling anticlockwise. Whilst there is no toll fee for using the M25, drivers must pay to use either of the crossings. An automatic number plate recognition charging scheme known as the 'Dart Charge' began in November 2014 to replace toll booths. Drivers must pay the charge online or face a fine. As of 2021, fees range between £2 and £6 depending on the type of vehicle.

Since the M25 opened in 1986, house prices in the area have risen by at least 300%. This is due to an increase in commuters to London as journey times have significantly lessened. Those using the Dartford Crossing may dispute the reduced journey time due to frequent traffic jams and long tailbacks.

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