M3 motorway (Great Britain)

M3 shield

Looking south at Twyford Down
Route information
Part of
Maintained by Highways England
Length59 mi (95 km)
HistoryOpened: 1971
Completed: 1995
Major junctions
Northeast endSunbury-on-Thames
51°25′00″N 0°25′26″W / 51°25′00″N 0°25′26″W / M3 motorway (northeastern end))
 Junction 2.svg UK-Motorway-M25.svg
J2 → M25 motorway
Junction 14.svg UK-Motorway-M27.svg
J14 → M27 motorway
Southwest endChilworth
50°57′16″N 1°24′29″W / 50°57′16″N 1°24′29″W / M3 motorway (southwestern end))
CountiesSurrey, Hampshire
Road network

The M3 is a motorway that runs from Sunbury-on-Thames, Surrey, to Southampton, Hampshire, a distance of approximately 59 miles (95 km). Via its feeder the A316, the route is one of five roads of dual carriageway width or greater into the southern half of London. It also provides access to major towns and cities along its route, principally the Aldershot Urban Area, Basingstoke, Winchester and Southampton.

It was constructed as a dual three-lane motorway except for its two-lane section between Junctions 8 (A303) and 9. The motorway was opened in phases, ranging from Lightwater/Bagshot to Popham in 1971 to Winchester to Otterbourne Hill in 1995. The latter stages attracted opposition from environmental campaigns across Britain due to its large cutting through wooded Twyford Down; numerous road protests were held which delayed its opening. Similar protests were avoided on the near-parallel A3 by construction of the Hindhead Tunnel. Since completion, the motorway has been an artery to the west and mid sections of the South Coast and Isle of Wight including for tourism. The major settlements nearest to the motorway are served by a railway also used for commuting but are relatively dispersed. Traffic on the M3 sees delays and congestion on its busiest sections near commuting hotspots and during holiday periods. From Chertsey to Fleet the road was in 2017 upgraded to a Smart Motorway, turning the hard shoulder into a permanent fourth lane with emergency refuge lay-bys. [1]


M3 motorway at East Stratton
Southern end of the M3 motorway, meeting the A33 at Southampton
M3 motorway at Fleet
The M3 under construction at Twyford Down

Originally approved as the "London to Basingstoke Motorway" with delays over funding for an extension to Southampton[2] the road was built to relieve two single carriageway trunk roads that were congested.[n 1][3]

In 1967, sections of the A33 road from Popham, Hampshire, to a northeastern point of the Winchester Bypass were widened to dual carriageways; this only partially alleviated growing congestion, especially in Winchester, which led to the southern phase gaining approval.[n 2][3]

Eastern section

The eastern section, from Sunbury-on-Thames in Surrey to Popham near Basingstoke opened in sections: first the Hampshire section in 1971, and then the Surrey section in 1974.[4] The cost for this first phase was £46m.[5] The completed road acts as a continuation of the A316 Country Way, an express three-lane road from Apex Corner, Hanworth, in Greater London to Sunbury-on-Thames.

The section is one of five routes into the southern half of London which reach Inner London with at least a dual-carriageway of dual-direction road, the others being the A3 (M), the A30/A4, the M20 and A2, however approximately one mile before reaching Inner London is combined with the routes of the A30 and M4 approaches.

Southern section

A first public inquiry for the "M3 London to Basingstoke Motorway: Popham to Compton extension" centred on the section passing Winchester, and was held in 1971, after which the ministry was instructed to reconsider and reconsult on the proposals.[6][7] A second public inquiry was held in 1976–77.[8][9] The earlier decision to route the motorway through or alongside the water meadows between St Catherine’s Hill and the compact cathedral city was reopened, and during the year-long inquiry the headmaster of Winchester College was forcibly ejected along with others for causing a disturbance.[7]

The scope of the M3 extension was reduced to defer the difficult decision about the section around Winchester and it was built in two sections (from 'Popham to Bridget's Farm' and from 'Bridget's Farm to Bar End') in 1995.[4] When this opened, the temporary junction to the A33 parallel route was removed.

The section of the M3 from near Junction 12 (Eastleigh and Chandler's Ford) to the last, Junction 14 for the M27 replaced part of the A33 road which was upgraded to motorway standard and opened in 1991.[7]

In 2008 the busiest section of the motorway, at Chandler's Ford, carried a daily average of around 130,000 vehicles.[10]

The southern section starts as a continuation of a single-lane avenue, Bassett Avenue and The Avenue in the City of Southampton as the M27 motorway provides alternative routes from other parts of the city, particularly its waterfront and downtown peak-hour accessway, the M271 motorway and Mountbatten Way providing dual to three lane highways starting at the northwest of the city.

Abandoned/suspended proposals

Its service station was envisaged at Basingstoke upon the motorway's completion but not built – superseded by one just north of Fleet and another north of Winchester.[11] Plans for a Basingstoke Services were again published in November 2017 [12]


An additional junction, numbered 4A, opened in April 1992 for Fleet.[13]

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