Upgrade of several sections of the M25 to Smart Motorway between junctions 10 (the A3 at Wisley) and 16 (the M40 at Denham).
The M25 already has some Smart Motorway technology along this full length, and was in fact the first motorway in the UK to have Variable Speed Limits, which have been operational here for at least 20 years. This scheme is therefore not a standard Smart Motorway project, and instead it will introduce All Lane Running at four specific locations:
- Junctions 15 to 16, providing five continuous running lanes between the M4 and M40
- Through junction 10 (A3 at Wisley)
- Through junction 11 (A317 Chertsey)
- Through junction 12 (M3 at Thorpe)
At present, the M25 has four running lanes from junctions 10 to 12, constructed as part of a standard widening scheme in the 1990s, but the fourth lane is dropped at each of those junctions so there are only three lanes between the exit and entry sliproads. This causes significant congestion, so the effect of the scheme will be to provide four continuous running lanes throughout.
On completion of the scheme the M25 will have four or more uninterrupted lanes from junction 7 (M23 at Merstham) to junction 20 (A41 at King's Langley).
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