At the time of opening it was the world’s largest ring road at 117miles (188km). It is now the second largest.
The pictures above are from a booklet issued by the Department of Transport to celebrate the engineering achievements of the road’s construction. Including one of the bridges at Runneymeade designed by Arup. The bridge was designed to match one already in place designed by Sir Edwin Lutyens.
Joe Moran commented in the Guardian that: “the inauguration of the M25 was the last major road-opening to generate real public excitement. The queues at both ends of the final section were much longer than usual because drivers were itching to be the first to complete an orbit.”