M4 motorway
Route information
Part of E30
Length:	191.9 mi (308.8 km)
Existed:	1961 – present
History:	Constructed 1961–1996
Major junctions
From:	Chiswick 51°29′23″N 0°16′41″W / 51.4897°N 0.2781°W / 51.4897; -0.2781 (M4 motorway (eastern end))
	M25 motorway A308(M) motorway A404(M) motorway A329(M) motorway M32 motorway M5 motorway M48 motorway M49 motorway M48 motorway A48(M) motorway
To:	Pont Abraham services 51°44′42″N 4°03′54″W / 51.7451°N 4.0651°W / 51.7451; -4.0651 (M4 motorway (western end))
Location
Primary destinations:	Hounslow, Hammersmith, Heathrow Airport, Ealing, Richmond, Uxbridge, Wembley, Harrow, Slough, Maidenhead, Reading, Newbury, Swindon, Marlborough, Chippenham, Bristol, Newport, Cwmbran, Cardiff, Bridgend, Port Talbot, Swansea, Neath, Llanelli, (Bracknell), (Basingstoke), (Oxford), (Cirencester), (Bath), (Chepstow), (Merthyr Tydfil), (Carmarthen), (Abergavenny), (Llandeilo), (Trowbridge)
Road network
Roads in the United Kingdom Motorways • A and B road zones

The M4 motorway links London with South Wales. It is part of the unsigned European route E30. Other major places along the route include Reading, Swindon, Bristol, Newport, Cardiff and Swansea. Originally referred to as the London-South Wales Motorway, the English section was constructed between 1965 and 1971, the Welsh section was completed in 1993 and the Second Severn Crossing opened in 1996.

The M4 runs close to the A4 from London to Bristol. After crossing the River Severn it follows the A48 through South Wales, using the Brynglas Tunnels at Junction 25a, Newport and terminates just north of Pontarddulais. The route of the M4 is known as the M4 corridor.

History[link]

The original bridge over River Neath (the A48), is to the right, the new M4 bridge is to the left

A new road from London to South Wales was first proposed in the 1930s, and the Ministry of Transport announced plans for the M4 as one of the first major post-war trunk road improvement projects in 1956.^[1]

The Chiswick Flyover opened in 1959.^[2] However it was not originally classed as a motorway.^[3] The Maidenhead bypass opened in 1961 whilst J1-J5 opened in 1965. From J18 to the west of Newport was opened in 1966 and included the Severn Bridge (now part of the M48). 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, and it was only following the creation of the Welsh Office that the Government became committed to a high-standard dual carriageway to Pont Abraham in Carmarthenshire.^[4]

The Second Severn Crossing

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.^[5] The Welsh section was completed in 1993, when the Briton Ferry motorway bridge opened. The Second Severn Crossing opened in 1996, together with new link motorways on either side of the estuary to divert the M4 over the new crossing. The existing route over the Severn Bridge was redesignated the M48, and the new M49 was opened to connect the new crossing to the M5.^[6]

In June 1999 the section of the third lane (the lane nearest the central reservation) between junctions 2 and 3 was converted to a bus lane and opened as a pilot scheme. The scheme was made permanent in 2001. A lower speed limit was introduced along the bus lane section at the same time.^[7] The bus lane was scrapped at the end of 2010 and the third lane was returned to all-traffic use.^[8]

In April 2005 speed checks carried out by police camera vans between junction 14 and junction 18 resulted in a public protest, involving a go-slow of several hundred vehicles along the affected sections of the motorway.^[9]

Between 2007 and January 2010 the section from Castleton (Junction 29) to and Coryton (Junction 32) was widened to 6 lanes.^[10] The scheme was officially opened in 25 January 2010 by the Deputy First Minister. Subsequent to opening there were occasional works with associated lane restrictions.^{[citation needed]}

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.^[11] A similar claim was made for a 30-mile (48 km) section of road in Scotland close to Aberdeen in September 2009 with refueling points at Bridge of Don, Ellon and Peterhead.^[12]

In October 2010 the new transport secretary, Philip Hammond announced that the bus lane would be suspended for 18 months from 24 December 2010 to be brought back for the 2012 Summer Olympics after which it was likely to be scrapped permanently.^[13]

Between 2008 and 2010, Junction 11, near Reading, was extensively remodelled with a new four-lane motorway junction and the construction of two extra road bridges around the existing junction and other works.^[14] The £65m scheme included work to the Mereoak roundabout and part of the A33 Swallowfield Bypass in Shinfield conversion, and also the conversion of the two existing bridges, one of which is available only for pedestrians and cyclists and the other for buses.^[15] It also involved the movement of the local Highways Agency and Fire Service offices, a long footbridge network being constructed, a special bus-lane and a new gyratory. Sound barriers for nearby residential areas were also installed.^[16] 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.^[17]

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Features[link]

Toll bridge[link]

The westbound carriageway tolls (left) and the 3-lane eastbound carriageway

The M4 crosses the River Severn via a toll bridge, the second of only two on the UK motorway network – the first was the original Severn Bridge, now part of the M48. Tolls in Wales are charged in one direction only - westbound. Drivers therefore have to pay to enter Wales, but not to enter England.

Speed limits[link]

For the majority of its length, the speed limit is the national speed limit. Exceptions include the following:

• 40 miles per hour (64 km/h) on the elevated section within London in both directions.
• 60 miles per hour (97 km/h) between the Heathrow turnoff and the elevated section eastbound only
• 50 miles per hour (80 km/h) when approaching the toll plaza on the Severn Crossing to protect tolling staff moving between the tolling booths,^[18]
• 50 miles per hour (80 km/h) on the Port Talbot elevated section between junction 40 and junction 41.

M4 bus lane[link]

M4 bus lane near Norwood Green, Ealing

There was a controversial 3.5-mile (5.6 km) bus lane on the eastbound (London-bound) carriageway from junction 3 (A312) to the start of the elevated 2-lane section near Brentford, covering part of the 15-mile (24 km) journey between Heathrow Airport and central London. The lane which had no intermediate exits was for use by buses, coaches, motorbikes, emergency vehicles and licensed taxis but not mini-cabs.^[19] It was used by 7% of vehicles which carried 21% of the people.^[7]

The lane was restored for normal motorway running at the end of 2010 for 18 months^[8] using a Experimental Traffic Order^[20] and will be re-established for the duration of the 2012 Summer Olympics with the intention that it will then be removed permanently.^[8]

Porous road surface[link]

Near Junction 35, there is a stretch of the motorway that has a surfacing of porous asphalt that improves drainage and reduces noise. When driving in heavy rain drivers notice a reduction in road spray from other vehicles and improved visibility. This special surface was publicised in an episode of the BBC's Tomorrow's World programme. This was the site of the first trial of the new road surface when it was laid down in 1993.^[21]

Elevated and heated section[link]

The elevated section in West London, built in the 1960s, is mostly directly above the A4 and extends over parts of Brentford's Golden Mile. This section was designed to have a heated road surface to reduce icing in winter, however, due to the high costs in preventing icing by this method the heating is no longer used.^{[citation needed]}

Four level stack interchanges[link]

M4 Junction 4B / M25 Junction 15 near Heathrow Airport

It has two of only three four-level stack interchanges in the UK, including the first UK example at the junction with the M5 (J20/"Almondsbury Interchange") and the other at the junction with the M25 (J4B). Junction 4B also has to make provision for a railway line passing beneath the M4. Due to the nature of such junctions, it is impossible to make a U-turn at J20 or J4B.

Tunnels[link]

The M4 passes through the Brynglas Tunnels at Junction 25a, Newport.

This is the only two–bored tunnel on the United Kingdom motorway network.

Notable junctions[link]

Junction '8/9' (the only one in the UK with dual-numbers) is the turn off for Maidenhead, Berkshire.

West of junction 13 on the eastbound carriageway there are a set of sliproads signposted "Works Unit Only". The signs have red borders, implying a military exit. It is a back entrance to RAF Welford, a Second World War airfield and now an RAF/USAF military installation mainly used for storing munitions. The M4 entrance allows easier access for the large vehicles used to carry the munitions.

Junction 27 (High Cross) is a normal grade-separated roundabout junction. However the on-bound slip roads point in the opposite direction to the intended direction of travel. Due to the topology of the landscape, both sets of slip roads are conjoined on either side of the roundabout. To travel westbound the driver must use an eastbound-facing slip road before looping around 180 degrees to join the westbound carriageway.

Junctions 30-31 (East Cardiff) were set aside for intermediate additional interchanges at the time on construction. Junction 30 (Cardiff Gate) has since been added but there are no current plans to construct Junction 31 (A469 road).

Junction 39 does actually exist, but can only be used to access the motorway from a single slip road onto the westbound carriageway from the A48 at junction 38. There is no exit from the motorway at this junction.

Junction 41 refers to two different junctions in two different directions, their movements not complementary. In the westbound direction, 41 is indicated as a spur leading to the roundabout in Briton Ferry formerly known as 41A, and the original bridge over the River Neath, which would allow access onto the stretch of the M4 from junction 43 westward. In the eastbound direction, 41 is indicated as an exit-only route to the A48 towards Port Talbot. As a result, it is possible in both directions to travel almost 2 miles (3.2 km) in the same direction having both joined and subsequently left the motorway at "Junction 41".

Junction 44 is unusual in that the eastbound entrance dives under the inside of the junction, effectively a creating a "right-turn" on a roundabout.

Current developments[link]

J19-J20 Managed Motorways[link]

Work is currently taking place to install^[22]Hard Shoulder Running on the M4 between junctions 19 and 20, and is estimated for completion in 2014.^[23]

Variable speed limit scheme between Junctions 24 and 28[link]

During construction of the electronic indicator signs for the variable speed limit scheme at junction 27 and a new concrete reservation

The variable speed limit scheme between junction 24 and junction 29 opened in June 2011.^[24] This section of the motorway was originally built in 1967 and has many non-standard gradients and a number of tight bends. It is hoped the flow of traffic will be smoothed and motorway capacity increased for the 8 miles (13 km) between the two junctions. The scheme should also save money through fewer accidents in the long term. Widening this section of the motorway is not possible because of the two-lane Brynglas Tunnels and existing housing close to the motorway.^[25]

Proposed developments[link]

M4 Junction 31[link]

Plans for the "missing" Junction 31, also known as the Thornhill interchange, which was originally granted planning permission in September 1991 (but subsequently expired) have been rekindled after proposals for a new business park on a 125 acres (51 ha) site north of the M4 were submitted to Cardiff Council.^[26] The developers of the business park, St Modwen Developments, would likely fund the new junction, which would be on the A469.^[27]

Other proposals[link]

Plans for an 'M4 Relief Road' around Newport were first announced by the Welsh Office in 1991, but made little progress. The Welsh Assembly Government revived the scheme as the 'New M4' tolled bypass in 2007^[28] but later abandoned it for financial reasons. An extension to the Newport Southern Distributor Road through the old Corus steel works is being considered.^[29] This road is already a dual carriageway but not open to the public. A public consultation exercise on options for improving the capacity of the M4 corridor around Newport opened on 5 March 2012. Its website states that:^[30] "the motorway around Newport does not conform to today’s motorway standards. It lacks continuous hard shoulders, has closely spaced junctions with sub-standard slip road visibility and narrows to a restricted two lane section through the Brynglas Tunnels. Heavy congestion occurs along this stretch and either side of it at peak hours."

There have been calls to close the slip roads at Junction 40 and 41 (at Port Talbot) to improve traffic flow. The motorway is only two lanes in this stretch and is a major traffic congestion blackspot. Junctions 40 and 41 (at Port Talbot) have very short slip roads which are not up to modern standards.^[31] The Port Talbot peripheral distributor road is under development, which should divert local traffic away from the M4. In future, it is hoped to extend the M4 to Carmarthen, but this depends on financing.^{[citation needed]} A new Junction, 15A, is being considered by Wiltshire Council and this would give access to South and Central Swindon as well as to Wroughton, Marlborough and Devizes via the existing A4361, as well as a possible Junction 18A which would connect with the A432 and A4174 giving better access to Bristol, via Mangotsfield, and also a direct link with Yate.^{[citation needed]}

Notable events[link]

• In June 1984 a crash near Maidenhead resulted in 13 deaths.^[32]

• In March 1991 Ten people died in a series of crashes in 1991 involving 51 vehicles near Hungerford.^[32]

• In May 1995 a coach carrying Royal British Legion members left the road close to the Severn Bridge resulting in 10 deaths.^[32]

Junctions[link]

Coordinate list

1. ^ 51°29′22″N 0°16′40″W / 51.48944°N 0.27778°W / 51.48944; -0.27778 (Start of M4) Eastern end of M1
2. ^ 51°29′41″N 0°29′44″W / 51.49472°N 0.49556°W / 51.49472; -0.49556 (Junction 5b of M4) Intersection of M25 and M4
3. ^ 51°27′14″N 1°18′52″W / 51.45389°N 1.31444°W / 51.45389; -1.31444 (Junction 13 of M4) Intersection of M4 and A34(E05)
4. ^ 51°33′01″N 2°33′11″W / 51.55028°N 2.55306°W / 51.55028; -2.55306 (J20 of M4) Almondburty Interchange - Intersection of M4 and M5
5. ^ 51°34′21″N 2°41′31″W / 51.5725°N 2.69194°W / 51.5725; -2.69194 (M4 Severn Crossing) Second Severn Crossing
6. ^ 51°44′42″N 4°03′54″W / 51.745°N 4.065°W / 51.745; -4.065 (End of M4) Western end of M1

See also[link]

Media related to M4 motorway at Wikimedia Commons

• New M4
• M4 Thames Bridge, Maidenhead
• A404(M) motorway
• M4 corridor
• List of motorways in the United Kingdom
• A48(M) motorway
• Transport in Wales

References[link]

External links[link]

Wikimedia Commons has media related to: M4 motorway

• CBRD Motorway Database - M4
• British Road Database: Motorways - M4 Junction 8/9
• The Motorway Archive
  • Junctions 1 to 5
  • Junctions 5 to 7
  • Junctions 8 to 14
  • Junctions 14 to 21
  • Junctions 21 to 23
  • Junctions 23 to 49

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