M4 motorway

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M4 motorway
Length	189.5 miles 305.0 km
Direction	East - West
Start	London Chiswick
Primary destinations	West London (Hounslow) Heathrow Airport Slough Maidenhead Reading Newbury Swindon Chippenham Bristol Newport Cwmbran Cardiff Bridgend Port Talbot Neath Swansea Llanelli
End	Pont Abraham services
Construction dates	1961 - 1996
Motorways joined	4B - M25 motorway 8/9 - A308(M) motorway 8/9 - A404(M) motorway 10 - A329(M) motorway 19 - M32 motorway 20 - M5 motorway 21 - M48 motorway 22 - M49 motorway 23 - M48 motorway 29 - A48(M) motorway
Euroroute(s)	E 30

The M4 motorway is a motorway in Great Britain linking London with Wales. It is part of the unsigned European route E30. Other major places directly accessible from M4 junctions are Reading, Swindon, Bristol, Newport, Cardiff and Swansea.

The M4 runs close to the A4 from London to Bristol. After crossing the Severn it follows the A48 through Wales, until its termination just north of Pontarddulais.

[edit] Special features

In London, the eastbound (London-bound) M4 carriageway has a bus lane from junction 3 until the elevated section. This lane caused some controversy when it was created.^[1] However, the bus lane has improved traffic flow onto the 2-lane elevated section which follows it.^{[citation needed]} There is some speculation that the original plan involved closing one lane from junction 3 to the elevated section to prevent congestion caused by the filtering of three lanes of traffic into two (the motorway is already temporarily down to two lanes at junction 3 because the left lane is exclusively for traffic leaving the motorway, so the effect of the bus lane is to make the 3-to-2 lane-transition seamless). Making the "spare" lane available for buses - and now taxis and motorcycles - was an afterthought.^[2]

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 has a heated road surface to reduce icing in winter.

The motorway is the only one in the UK to feature a 'dual-numbered' junction. Junction '8/9' is the turn off for Maidenhead, Berkshire.

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). Both are impressive feats of engineering, particularly junction 4B which also has to make provision for a railway line passing beneath the M4. However, due to the nature of such junctions, drivers should bear in mind that it is impossible to make a U-turn at J20 or J4B.

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 (the original route of the M4, now the M48).

There is a special slip road west of the A34 to Newbury from the eastbound carriageway which leads to RAF Welford. This slip road is enigmatically signposted, in red lettering, "Works Unit Only".

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 conditions drivers notice a reduction in spray from other vehicles and improved visibility. This special surface was publicised in an episode of the BBCs Tomorrow's World programme. This was the site of the first trial of the new road surface when it was laid down in 1993^[3].

[edit] Speed checks

Speed checks are carried out between junction 14 and junction 18 (in both directions). These are carried out by police camera vans situated on bridges over the motorway. These measure the speed of vehicles using laser detection equipment. The introduction of these measures proved controversial and resulted in a public protest, involving a go-slow of several hundred vehicles along the affected sections of the motorway during April 2005.^[4]

Traffic heading into London travels at a maximum speed of 60 mph (97 km/h) after the Heathrow turnoff, the limit is enforced by cameras. The elevated section is also enforced by speed cameras at 40 mph (64 km/h). Traffic heading out of London is limited to 40 mph (64 km/h) on the elevated section, but there are no cameras.

Speed checks are also carried out by mobile Safety Camera Partnership vans on the toll plaza on the Welsh side of the M4 after the Second Severn Bridge. There are also mobile camera vans on sections of the M4 between the toll plaza and Cardiff.

Between Junction 34 and Junction 37, there are three bridges crossing over the motorway. These three bridges sometimes have mobile speed camera vans parked on them to catch speeding motorists on the motorway below. These bridges are located on fairly sharp bends in the motorway.

The section between junction 40 and junction 41 has a maximum speed of 50 mph (80 km/h), and is enforced by a permanent speed camera (Gatso), to be found near junction 41 (in both directions).

[edit] Junctions

The M4 between junctions 22 and 23, crossing the River Severn from England to Wales on a cable-stayed bridge (the Second Severn Crossing). Wales is seen in the distance.

The M4 near Bristol (England) between junctions 19 and 20, looking west towards Wales.

[edit] Notes

During the construction of the section around Cardiff in 1980, junction numbers were set aside for intermediate interchanges that were not built at the time. 33 had been set for the link road to the west (A4232), 32 for the A470, with 31 intended for the A469 to Caerphilly, and 30 for the great "Hook Road" - a plan which was later shelved. Junction 30 was later added to serve the link road in the east, which will eventually form a ring road from junctions 33 to 30, via Cardiff Bay. Number 31 remains unused as of 2006, and there are no immediate plans to build a junction with the A469.

Contrary to popular belief, junction 39 does exist. However, it consists of a single slip road completing the missing movement onto the westbound carriageway from the A48 at junction 38, thus 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 km) in the same direction having both joined and subsequently left the motorway at "junction 41".

As of spring 2007, the stretch between Junction 29 Castleton and J32 Coryton is being widened to 3 lines either side in order to relieve congestion that plagues this stretch. Work is expected to take 2 years.

Plans are progressing for the M4 Toll Newport bypass, scheduled for completion by 2014.

[edit] M4 people

• Sam Hammam - owner of Cardiff City football club - caught driving at 93mph and banned from driving for six months by Pontypridd magistrates court in April 2004.
• Harriet Harman - caught at 99mph in Wiltshire and banned from driving for six days by North Wiltshire magistrates court in February 2003.
• Gavin Henson - caught at 110mph and banned from driving for a month by Chippenham magistrates court in October 2006.
• Neil Kinnock - caught at 57mph in a 40mph section of roadworks, and banned from driving for six months by Abergavenny magistrates court in April 2006.
• Cozy Powell - died on April 5, 1998 following a car crash, driving his Saab 9000 in bad weather while talking to his girlfriend on a mobile phone.

[edit] See also

• M4 Toll
• A404(M) motorway
• M4 corridor
• List of motorways in the United Kingdom

[edit] References

1. ^ "M-way bus lane gets green light", BBC, 2001-01-16.
2. ^ M4 Bus Lane. CBRD.
3. ^ http://www.hanson.biz/files/pdf/magazine/2006/2006Q4_op.pdf
4. ^ "Drivers hold M4 speed camera demo", BBC News, April 30, 2005.

[edit] External links

• 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

	Motorways in the United Kingdom
Great Britain: M1 • M2 • M3 • M4 • M5 • M6 • M6 Toll • M8 • M9 • M10 • M11 • M18 • M20 • M23 • M25 • M26 • M27 • M32 • M40 • M42 • M45 • M48 • M49 • M50 • M53 • M54 • M55 • M56 • M57 • M58 • M60 • M61 • M62 • M65 • M66 • M67 • M69 • M73 • M74 • M77 • M80 • M90 • M180 • M181 • M271 • M275 • M602 • M606 • M621 • M876 • M898
A1(M) • A3(M) • A38(M) • A48(M) • A57(M) • A58(M) • A64(M) • A66(M) • A74(M) • A167(M) • A194(M) • A308(M) • A329(M) • A404(M) • A601(M) • A627(M) • A823(M)
	Northern Ireland: M1 • M2 • M3 • M5 • M12 • M22 • A8(M)	edit
Past: M41 • M63 • A18(M) • A40(M) • A41(M) • A102(M) • A6144(M)    Unbuilt: M12 • M15 • M31 • M64    Future: M4 Toll