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
West London Orbital most modern standards". The transit time from Brent Cross to Surbiton was quoted as 28 minutes, with a maximum train speed of 80 km/h. The promoters cited a number of reasons why they believed an underground scheme would be cost-effective at £1.75bn: with lower tunnelling costs as the tunnel diameter would be smaller than for a heavy rail scheme; there are no other rail tunnels to avoid (as in central London); and the subsoil strata are suitable for modern tunnel boring machines (TBMs). A number of other notable orbital rail schemes for London have been previously proposed: West London Orbital