Police were forced to close part of the clockwise M25 on Sunday after the road surface started melting
The clockwise carriageway at junction 23, near Potters Bar, was closed for resurfacing work to be carried out on the softened tarmac surface, which had started to melt in soaring temperatures with a ridge forming in the road.
The effects of temperatures above 50C on tarmac surfaces depend on a variety of factors and are not uniform across the strategic road network. More technical information is available on the BBC News website.