As the M25 celebrates its 25th birthday, Sally Boazman takes a road trip to see how the motorway has changed our economy, environment and living habits.
The 117-mile orbital road took more than 11 years to build. It cost £1bn, and used more than 2m tons of concrete and 3.5m tons of asphalt.
The final section was opened by Prime Minister Margaret Thatcher in October 1986 to a huge fanfare.
Sally Boazman charts the M25's history, follows the team that keeps it moving, and meets a couple who even got married on it.