The M4, originally the London-South Wales Motorway, is the third-longest motorway in the United Kingdom, running from West London to West Wales. The English section to the Severn Bridge was constructed between 1961 and 1971; the Welsh element was largely complete by 1980, though a non-motorway section around Briton Ferry bridge remained until 1993. On the opening of the Second Severn Crossing in 1996, the M4 was rerouted over it. The line of the motorway from London to Bristol runs closely in parallel with the A4. After crossing the River Severn, toll-free since December 2018, the motorway follows the A48, to terminate at the Pont Abraham services in Carmarthenshire. The M4 is the only motorway in Wales apart from its two spurs: the A48(M) and the M48. The major towns and cities along the route—a distance of approximately 189 miles (304 km)—include Slough, Reading, Swindon, Bristol, Newport, Cardiff, Bridgend, Port Talbot and Swansea.
History A new road from London to South Wales was first proposed in the 1930s. In 1956 the Ministry of Transport announced the plans for the first major post-war road improvement projects. The Chiswick flyover, a short section of elevated dual-carriageway, not originally classed as a motorway, opened in 1959 to reduce the impact of traffic travelling between central London and the west.
The Maidenhead bypass (J7–J9) opened in 1961, the section from Slough to Maidenhead (J5–J7) opened in 1963 and J1–J5 opened on 24 March 1965, incorporating the Chiswick flyover. The stretch from J18 to the west of Newport was opened in 1966, including the Severn Bridge.
The Port Talbot by-pass, also built in the 1960s and now part of the M4, was originally the A48(M) motorway, a number now allocated to a short section of motorway near Cardiff. The Ministry of Transport originally intended that the M4 would terminate at Tredegar Park west of Newport, but following the creation of the Welsh Office the government became committed to a high-standard dual carriageway to Carmarthenshire.
The English section of the motorway was completed on 22 December 1971 when the 50-mile (80 km) stretch between junctions 9 and 15 (Maidenhead and Swindon) was opened to traffic. The Welsh section was largely completed between 1970 and 1980, though a non-motorway section remained across the Briton Ferry bridge until 1993, when a second motorway-only bridge opened. In 1996, the Second Severn Crossing opened with new link motorways on either side of the estuary to divert the M4 over the new crossing. At the same time, the original route over the Severn Bridge was redesignated the M48, and the M49 was opened to link the new crossing with the M5 at Avonmouth. The new M49 shortened the route between South Wales and the South West, and reduced traffic at the busy M4/M5 junction at Almondsbury.
After completion In April 2005, speed checks carried out by police camera vans between junction 14 and junction 18 led to a public protest, involving a "go-slow" of several hundred vehicles along the affected sections of the motorway. Between 2007 and January 2010, the section from Castleton (junction 29) to Coryton (junction 32) was widened to six lanes. The scheme was formally opened on 25 January 2010 by Ieuan Wyn Jones the Deputy First Minister for Wales. During 2009, the Newport section of the motorway between junctions 23a and 29 was upgraded with a new concrete central barrier. In February 2010, it was proposed that the M4 in South Wales would become the first hydrogen highway with hydrogen stations provided along the route, with an aspiration for further stations to be provided along the M4 into South West England over time. Between 2008 and 2010, junction 11 was extensively remodelled with a new four-lane junction, two new road bridges and other works. The £65 million scheme included work on the Mereoak roundabout and part of the A33 Swallowfield Bypass near Shinfield, and also the conversion of the two existing bridges, one of which is available only to pedestrians and cyclists and the other to buses. It also involved the movement of the local Highways Agency and Fire Service offices, and the construction of a long footbridge network, a new bus lane and a new gyratory. Sound barriers for nearby residential areas were also installed. In April 2008, the decision to preserve a rare Vickers machine gun pillbox and turn it into a bat roost was announced by the developers.
Former bridge tolls Tolls were charged on the Severn Bridge(s) from opening until 2018. In 1966 the toll was 2s 6d (post-decimalisation equivalent £0.125) for cars, rising to £1 in the late 1980s. Around 1991 the toll was doubled, but charged in the westbound direction only, to reduce queuing. After 1996, the tolls were equal westbound-only on both bridges, and rose steeply after 2000 to a peak of £6.70 for cars in 2017, leading to protests from Welsh businesses. Tolls on both bridges over the River Severn were eliminated on 17 December 2018, and the former toll booths were removed in 2019.
Timeline of construction
Maintenance Maintenance of the Second Severn Crossing and the 123 miles (198 km) of motorway in England is the responsibility of National Highways. The 76 miles (122 km) in Wales is the responsibility of the South Wales Trunk Road Agent.
Features
Speed limits
For the majority of its length, the national speed limit applies. Exceptions include the following:
40 miles per hour (64 km/h) on the Chiswick Flyover within London in both directions. 60 miles per hour (97 km/h) between junction 4 and the Chiswick Flyover, eastbound only. 50 miles per hour (80 km/h) on the Port Talbot elevated section between junction 40 and junction 41. The fixed speed camera was removed in 2006 as it was believed to be causing tailbacks. In July 2014, an average speed camera system was installed; it generated around £500,000 in fines in the first six months. 50 miles per hour (80 km/h) between junctions 24 and 28 at Newport.
Smart motorway
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