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Merstham Interchange

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Merstham Interchange
Location Map ( geo)
Merstham Interchange at Night.jpg
The Junction at night.
Cameraicon.png View gallery (22)
Location
Merstham, Surrey
County
Surrey
Highway Authority
National Highways
Junction Type
Four Level Stack
Roads Joined
M23, M25

The Merstham Interchange is the junction between the M25 (for which it is junction 7), and the M23 (for which it is junction 8). It is one of three four-level stacks in the country. The M23 is carried over the M25 at a height of 23m by a five span steel box girder bridge.


When the junction was designed, the M23 and M25 had a through-junction cross section of a D3M, whilst the link roads had a 2 lane + hard shoulder cross section except on the bridges where they were only 2 lanes wide with no hard shoulder. Due to lack of historical accessible records & images it is hard to tell when the lanes at the junction were reduced, but it can be assumed for much of the M23's existence the M23 main line only ran as a D2M through the junction with an extra wide hard shoulder as the Northern section of the M23 was never built, meaning most traffic leaves to use the M25. All of the connecting link roads have ran as two lanes for the past 25+ years, except the M23S -> M25CW link which only has a single lane marked, likely due to low traffic & one of the tightest bend radiuses of the junction.

Two other bridges also spans over the motorways & link roads which are part of the local road network. These are Rockshaw Road & Warwick Wold Road.

In 2014 the M25 on both sides and through the junction was upgraded to an Smart Motorway (ALR to the East & CM to the West), however the slip roads reverted to a fixed speed limit shortly after the diverges.

When the M23 was upgraded to a smart motorway in 2019-2020 between Junction 8 (this junction) & Junction 10, the merge onto and diverge off of the M23 southbound was majorly modified. The diverge was widened from 2 lanes to 4 lanes, meaning that traffic heading in both directions onto the M25 had two lanes they could use instead of just one. The merge was also modified from 2 lanes (1 merge + 1 lane gain) to 3 lanes (1 merge + 2 lane gain). All of the slip roads except those leading to the M23 NB also got a variable speed limit during this time.

Opening

Ordnance Survey showed both the M23 J7 - J11 and M25 J6 - J8 and J7 Merstham Interchange as under construction on the 1974 1:50000 map (revised 1972), with anticipated opening dates of Spring 1974 for M23 and Autumn 1974 for M25. The dates must have slipped back. The M23 section through the interchange opened on 19 December 1974 per The Gazette with the M25 section and connecting slip roads opening on 10 February 1976 per The Gazette.


Routes

Route To Notes

M23

London, Croydon

M23

Brighton, Crawley, Gatwick Airport

M25

Heathrow Airport (M4), Watford & (M1)

M25

Dartford, Maidstone, M11 & M20

Strip Maps




Merstham Interchange
Related Pictures
View gallery (22)
M23-M25 Interchange - Coppermine - 879.jpgMerstham - Coppermine - 22785.jpgM23 junction - Coppermine - 3716.jpgM25 J7 - Coppermine - 1066.jpgM23-M25 Interchange in 1979 - Geograph - 2466993.jpg
Junctions on the M25 and related routes
M25 & A2821A Littlebrook • 1B Princes Road • 2 Darenth • 3 Swanley • 4 Hewitts Roundabout • 5 Chevening/Chipstead • 6 Godstone • 7 Merstham • 8 Reigate Hill • 9 Leatherhead • 10 Wisley • 11 Addlestone • 12 Thorpe • 13 Runnymede • 14 Poyle/Terminal 5 Roundabout • 15 Thorney • 16 Denham • HS2 Works • 17 Maple Cross • 18 Chorleywood • 19 Chandlers Cross/Hunton Bridge • 20 Kings Langley • 21 Chiswell • 21A Bricket Wood • 22 The Bell • 23 Bignell's Corner • 24 Potters Bar • 25 Waltham Cross • 26 Waltham Abbey • 27 Theydon Bois • 28 Brook Street • 29 Cranham • Ockendon • 30 Mar Dyke • 31 Purfleet
M26Chevening • Otford • 2A Wrotham Heath • 3 Addington
M16 'Ringway 3'Sunbury Cross • Yeading Lane • Oxhey Lane • Bushey • Bignell's Corner • Potters Bar • Waltham Cross • Waltham Abbey • Epping • Theydon Bois • Navestock • Brentwood • Brook Street • Cranham • Mar Dyke • Purfleet • Littlebrook • Princes Road • Darenth • Swanley
'Ringway 4'Addington • Wrotham Heath • Otford • Chevening • Westerham • Godstone • Merstham • Reigate Hill • Leatherhead • Wisley • Addlestone • Thorpe • Runnymede • Poyle • Thorney • Iver Heath • Denham • Maple Cross • Chorleywood • Sarratt • Hunton Bridge • Hoddesdon • Navestock
Junctions on the M23 and A23
A23 LondonKennington Oval • Streatham One-Way System • Thornton Heath Pond • Lombard Roundabout • Fiveways Corner • Purley Cross • Brighton Road Roundabout • Hooley
non primary A23Hooley • Lombard Roundabout • The Stations Roundabout • Belfry Roundabout • Longbridge Roundabout • Airport Way Roundabout West • Beehive Ring Road Junction • Gatwick Road Roundabout • Lowfield Heath Roundabout • Fleming Way Roundabout • Manor Royal Junction • Tushmore Gyratory • Ifield Roundabout • Ewhurst Roundabout • Gossops Green Junction • Cheals Roundabout • Southgate Roundabout • Pease Pottage Interchange
M23Unbuilt: 1 Tooting Bec/Streatham •  2 Streatham Vale • 3 Mitcham • 4 Beddington • 5 Wallington • 6 Woodmansterne   Built: 7 Hooley • 8 Merstham • 9 Gatwick • 10 Crawley • 10A Balcombe Road • 11 Pease Pottage
Airport WayAirport Way Roundabout West • 9a Airport Way Roundabout East • 9 Gatwick Interchange
A23 Sussex11 Pease Pottage • Handcross • Slaugham • Warninglid • Bolney Park Farm • Bolney • Hickstead • Sayers Common • Albourne Junctions • Hurstpierpoint • Newtimber • Quarry Junction • Dale Hill • Pyecombe • Patcham • Mill Road Roundabout
A23 BrightonMill Road Roundabout • Carden Avenue Roundabout • Crown and Anchor Junction • Preston Park South Junction • Beaconsfield Crossroads • Preston Circus • Ditchling Road Crossroad • Open Market • St Peters Church • Richmond Parade • North Road • Pavilion Parade • Old Steine • Grand Junction (Aquarium Junction)


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