The Almondsbury Interchange in South Gloucestershire, is one of the United Kingdom's largest motorway stack interchanges. The interchange is one of only three four-level stacks in the UK, spanning a range (including slip roads) of 1 km by 1 km. It is the interchange for the M5 at junction 15 and M4 at junction 20, and is situated at the northern fringes of Bristol close to the village of Almondsbury, the Aztec West industrial estate, and Bradley Stoke. When it opened in 1966, it was the most complex junction on the British motorway network, a free-flowing interchange on four levels. Since then traffic volumes have increased and at busy periods, the Interchange becomes more difficult to negotiate safely. A managed motorway project has been introduced in an effort to relieve congestion.