The motorway is around 10 miles (16 Kilometres) long and is one of the least busy parts of the British motorway system.
It was built in the late 1950s as part of a link from London to Birmingham. In the 1960s it was one of the busiest roads in Britain. However in 1972, the opening of the M6 provided a much faster route through to Birmingham from London. Most traffic diverted to this route, leaving the M45 with only a fraction of its previous traffic.