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 outside Heathrow Airport consistently records the highest number of daily traffic counts on the British strategic road network with a sample in 2017 measuring 211,059 counts (lower than the record peak measured in 2014 of 262,842 counts). This compares to 197,219 counts measured on the M1 motorway between junction 7 and 8 outside Hemel Hempstead in 2014, and 195,325 counts measured on the M60 motorway between junctions 12 and 13 in Western Manchester, also in 2014. The M25, plus the short non-motorway A282 which joins the two ends of the M25 across the River Thames using the Dartford Crossing, is