M25 motorway and Thurrock off junction 31 (to the east of London). Cobham services opened on 13 September 2012. Originally, the M25 was unlit except for sections around Heathrow, major interchanges and Junctions 23–30. Originally, low pressure sodium (SOX) lighting was the most prominent technology used, but widening projects from the 1990s onwards have all used high-pressure sodium (SON) lighting and this has diminished the original installations. By 2014 only one significant stretch was still SOX-lit (Junction 25–26) and the units were removed the same year. The motorway passes through five counties. Junctions 1A–5 are in Kent, 6–14 are in Surrey, 15–16
M25 motorway from in Potters Bar to in Byfleet. Three Greater London boroughs (Enfield, Hillingdon and Havering) have realigned their boundaries to the M25 for minor stretches; while in others, most notably in Essex and Surrey, the radial gap between Greater London and the motorway reaches , neither of which coincide with the Metropolitan Green Belt. Major towns listed as destinations (right), in various counties, adjoin the M25. North Ockendon is the only settlement of Greater London situated outside the M25. In 2004, following an opinion poll, the London Assembly mooted for consultation alignment of the Greater London boundary with the M25.