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
M40 motorway A412 southbound. The original line of the A40 can be seen going straight through the roundabout. The motorway carries on for another before it reaches J1a, the free-flow interchange with the M25 London Orbital. It is a partially unrolled cloverleaf, with the smoothest turns from the London-bound M40 (from Oxfordshire, Warwickshire and the wider West Midlands) to the anti-clockwise M25 (London Heathrow, Gatwick, The Channel Ports) and vice versa, since this is the largest exchange of traffic between the two motorways. The M40 passes over the interchange, with the M25 on the bottom. The clockwise M25 enters the junction with