With an altitude of 1,220 feet above sea level, it is Britain's highest motorway ' the motorway in the clouds. The Outlane to Windy Hill section opened in December 1970. The motorway was formally opened by The Queen in October 1971, with junction 24 ' at the Ainleys ' and junction 25 ' at Brighouse.
The Hartshead Moor service station was started in 1971. In February 1974, 12 people died and many were injured when a provisional IRA bomb destroyed a coach near the Chain Bar junction; the coach was carrying soldiers and their families back to Catterick.
Scammonden Bridge is the largest single-span bridge in Europe, and Scammonden Dam is the largest earth-filled dam in Europe. The motorway was designed by Colonel Stuart Maynard Lovell