M4 motorway

The M4 motorway links London with South 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. 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 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.

Contents

History

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

The M4 was built in several stages. In the 1960s two sections were built, one extending from the London end to near Maidenhead, one from north of Bath to west of Newport, including the Severn Bridge (opened in 1966 and 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 English section of the motorway was completed on 22 December 1971 when the 50 miles (80 km) stretch between junctions 9 and 15 (Maidenhead and Swindon) was opened to traffic[1]. 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.[2]

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.[3]

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.[4] A similar claim was made for a 30 mile section of road in Scotland close to Aberdeen in September 2009 with refueling points at Bridge of Don, Ellon and Peterhead.[5]

Features

The Second Severn Crossing
The M4/M25 motorway junction, near Heathrow Airport

Toll bridge

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 the M48. Tolls are charged in one direction only - westbound. Drivers therefore have to pay to enter Wales but not to enter England.

M4 bus lane

In London, the eastbound (London-bound) M4 carriageway has a bus lane, which opened in June 1999, from junction 3 until the elevated section. This lane caused controversy when it was created.[6] It continues to be criticized, with the AA noting that the lane is a clearly underused white elephant. The bus lane is barely enforced, with private drivers able to get away with regularly driving in it.[7] However, the bus lane has improved traffic flow onto the 2-lane elevated section which follows it. A study by the Transport Research Laboratory stated that the lane has reduced rush hour journey times by 3.5 minutes for buses and one minute for cars, even though the speed limit was cut from 70 miles per hour (110 km/h) to 50 miles per hour (80 km/h).[8] 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.[9]

Porous road surface

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.[10]

Elevated and heated section

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.

Four level stack interchanges

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

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

Notable junctions

Junction '8/9' (only one in the UK to feature a 'dual-numbered' junction) 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 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".

Speed limits

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

For the majority of its length the speed limit is the National speed limit. Exceptions include:-

Current developments

Current widening works (J29-J32)

M4 Junction 11 Improvement Scheme

Junction 11, near Reading, is in the process of being extensively developed with a new four-lane motorway junction and the construction of two extra road bridges around the existing junction and other works. Work started in 2008 and is expected to be completed by summer 2010.[13] The £65m scheme includes work to the Mereoak roundabout and part of the A33 Swallowfield Bypass in Shinfield conversion and the conversion of the two existing existing bridges, one of which be available only for pedestrians and cyclists and the only for buses.[14] It will also involve the movement of the local Highways Agency and Fire Service offices, build a long footbridge network, a special bus-lane and a new gyratory. It will also install sound barriers for nearby residential areas, some of which have already been completed.[15] 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.[16]

M4 J23a-J29 Upgrade

As of April 2009, the Newport section of the motorway between junctions 23a and 29 is being upgraded with a new concrete central barrier; from 2010, a variable speed limit will be introduced.[17]

M4 J29-J32 Widening

As of spring 2007, the stretch between Junction 29 Castleton and J32 Coryton is being widened to 6 lanes in order to improve journey reliability and add capacity. Work is expected to be completed by December 2009.[18]

On 25 January 2010 the Deputy First Minister officially opened the widened motorway. In spite of this there is still work going on and occasionally reduced lanes.

Proposed developments

M4 Junction 31

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.[19] The developers of the business park, St Modwen Developments, would likely fund the new junction, which would be on the A469.[20]

Other proposals

A 'New M4' tolled bypass for Newport was proposed in 2007[21] but later abandoned for financial reasons. An extension to the Newport Southern Distributor Road through the old Corus steel works is being considered.[22]. This road is already a dual carriageway but not open to the public.

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.[23] The Port Talbot peripheral distributor road is under development, which should divert local traffic away from the M4.

Junctions

Data[24][25][26] from driver location signs are used to provide distance and carriageway identification information. Where a junction span several hundred metres and the data is available, both the start and finish values for the junction are shown.

M4 Motorway
km Eastbound exits (B Carriageway) Junction Westbound exits (A Carriageway)
Road becomes A4 to Central London J1 North Circular A406
South Circular A205
Chiswick A315
Non-motorway traffic
11.8 A4 from Central London becomes the M4
Start of motorway
13.4
13.7		 North Circular A406
South Circular A205
Chiswick A315		 J2 Staines, Hounslow, Brentford A4
Heston services Services Heston services
21.5
22.1		 Heathrow (Terminals 4, 5 & Cargo), Hayes, Harrow, Hounslow A312 J3 Heathrow (Terminals 4, 5 & Cargo), Hayes, Harrow, Hounslow A312
24.5
25.2		 Heathrow (Terminals 1, 2 & 3) (A4)
Uxbridge (A408)		 J4a Heathrow (Terminals 1, 2 & 3) (A4)
Uxbridge (A408)
27.0
28.5		 Heathrow (Terminals 4, 5 & Cargo), Gatwick Airport, Watford, Oxford, Stansted Airport (M40, M1, M11, M3, M23) M25 J4b Heathrow (Terminals 4, 5 & Cargo), Gatwick Airport, Maidstone, Watford, Oxford, Stansted Airport (M40, M1, M11, M3, M23) M25
30.7
31.4		 Colnbrook, Langley A4
Eton, Datchet B470		 J5 Colnbrook, Langley A4
Eton, Datchet B470
36.8
37.4		 Slough (Central) A355
Windsor A322		 J6 Slough (Central) A355
Windsor A322
39.8
40.3		 Slough (West) A4 J7 Slough (West) A4
44.7
45.4		 High Wycombe, Henley A404(M)
Maidenhead A308(M)		 J8/9 High Wycombe, Henley A404(M)
Maidenhead A308(M)
56.4
57.6		 Reading (East), Wokingham, Bracknell A329(M) J10 Reading (East), Wokingham, Bracknell A329(M)
65.4
66.3		 Basingstoke, Reading (Central) A33 J11 Basingstoke, Reading (Central) A33
Reading services Services Reading services
72.9
73.5		 Reading (West), Theale A4 J12 Reading (West), Theale A4
91.5
92.1		 Newbury, Oxford A34
Chieveley services		 J13
Services		 Newbury, Oxford A34
Chieveley services
103.7
104.3		 Hungerford, Wantage A338 J14 Hungerford, Wantage A338
110.5 Membury services Services Membury services
122.9
124.0		 Swindon (East) A419
Marlborough A346
Oxford (A420)		 J15 Swindon (East), Gloucester A419
Marlborough A346
132.6
133.2		 Swindon (West), Wootton Bassett, RAF Lyneham, Calne A3102 J16 Swindon (West), Wootton Bassett, RAF Lyneham, Calne A3102
152.5
153.4		 Chippenham A350
Cirencester A429		 J17 Chippenham A350
Cirencester A429
155.7 Leigh Delamere services Services Leigh Delamere services
168.8
170.0		 Bath, Stroud A46 J18 Bath, Stroud A46
181.5
182.1		 Bristol M32 J19 Bristol M32
186.3
187.2		 The SOUTH WEST, Bristol (West), The MIDLANDS, Gloucester M5
Almondsbury Interchange		 J20 The SOUTH WEST, Bristol (West), Exeter, The MIDLANDS, Gloucester M5
Almondsbury Interchange
189.5
190.0		 No access J21 Chepstow M48
195.2
195.7		 Avonmouth M49
The SOUTH WEST, Bridgwater, Exeter (M5 South)		 J22 Avonmouth M49
ENGLAND
Second Severn Crossing
WALES
No tolls Tolls Toll Booth
206.4 Chepstow M48 J23 No access
Magor, Caldicot B4245
Magor services		 J23a
Services		 Magor, Caldicot B4245
Magor services
City centre A48
Newport B4237
Monmouth A449
The MIDLANDS (M50)		 J24 City centreA48
Newport B4237
Monmouth A449
No access J25 Caerleon B4596
No access J25a Newport, Cwmbran A4042
Brynglas Tunnels Tunnel Brynglas Tunnels
Newport, Cwmbran, Caerleon A4051 J26 Newport A4051
High Cross B4591 J27 High Cross B4591
Newport A48
Risca, Brynmawr A467		 J28 Newport A48
Risca, Brynmawr A467
No access J29 Cardiff East and South A48(M)
Cardiff East A4232
Cardiff Gate services		 J30
Services		 Cardiff East A4232
Cardiff Gate services
Cardiff North, Merthyr Tydfil A470 J32 Cardiff North, Merthyr Tydfil A470
Cardiff West, Cardiff International Airport, Barry, Penarth A4232
Cardiff West services		 J33
Services		 Cardiff West, Cardiff International Airport, Barry, Penarth A4232
Cardiff West services
Llantrisant, Rhondda A4119 J34 Llantrisant, Rhondda A4119
Pen-coed A473 J35 Pen-coed, Bridgend A473
Bridgend A4061
Maesteg A4063
Sarn Park services		 J36
Services		 Bridgend A4061
Maesteg A4063
Sarn Park services
Porthcawl, Pyle A4229 J37 Porthcawl, Pyle A4229
Port Talbot A48 J38 Port Talbot A48
No access J39 No access
Port Talbot A4107 J40 Port Talbot A4107
Port Talbot A48 J41 Port Talbot, Baglan A48
Swansea A483
Briton Ferry A48		 J42 Swansea A483
Neath, Merthyr Tydfil A465 J43 Neath, Merthyr Tydfil A465
Swansea A48 J44 Swansea A48
Swansea, Pontardawe, Morriston, Clydach A4067 J45 Swansea, Pontardawe, Morriston, Clydach A4067
Swansea, Llangyfelach B4489 J46 Swansea, Llangyfelach B4489
Swansea A483
Pontarddulais A48
Penllergaer, Gorseinon A4240
Swansea services		 J47
Services		 Swansea A483
Pontarddulais A48
Penllergaer, Gorseinon A4240
Swansea services
Pontarddulais, Llanelli A4138 J48 Pontarddulais, Llanelli A4138
Start of motorway J49
Terminus		 Carmarthen A48
Ammanford A483
Pont Abraham services

See also

References

  1. ↑ "On the road". The Motor nbr 3625: Page 30. 23 December 1971. 
  2. ↑ The Motorway Archive: M4 Second Severn Crossing
  3. ↑ "Drivers hold M4 speed camera demo". BBC News. 30 April 2005. http://news.bbc.co.uk/1/hi/england/wiltshire/4498551.stm. 
  4. ↑ "M4 in Wales to be 'hydrogen highway,' ministers to say". BBC News. 2010-02-12. http://news.bbc.co.uk/1/hi/wales/8511319.stm. Retrieved 2010-02-12. 
  5. ↑ "'Hydrogen highway' plans backed". BBC News. 2009-09-08. http://news.bbc.co.uk/1/hi/scotland/north_east/8245093.stm. Retrieved 2010-02-12. 
  6. ↑ "M-way bus lane gets green light". BBC. 2001-01-16. http://news.bbc.co.uk/1/hi/uk/1120542.stm. 
  7. ↑ "M4 bus lane is 'barely enforced'". BBC News. 11 September 2009. http://news.bbc.co.uk/2/hi/uk_news/england/london/8249919.stm. Retrieved 12 May 2010. 
  8. ↑ "Does this look like a U-turn?". BBC. 18 January 2001. http://news.bbc.co.uk/1/hi/uk/1119193.stm. Retrieved 12 May 2010. 
  9. ↑ Chris Marshall. "M4 Bus Lane". CBRD. http://www.cbrd.co.uk/indepth/m4buslane. 
  10. ↑ 2006 Fourth quarter foundation magazine - Operations and products
  11. ↑ "Speed cameras slow bridge traffic". BBC News. 5 October 2004. http://news.bbc.co.uk/1/hi/wales/south_east/3714770.stm. 
  12. ↑ "M4 Junctions 24 to 28 - Average Speed Cameras". Traffic Wales. http://www.traffic-wales.com/13837. Retrieved 2009-09-25. 
  13. ↑ "M4 Junction 11 Improvement Scheme". Highways Agency. http://www.highways.gov.uk/roads/projects/19089.aspx. 
  14. ↑ "M4 Junction 11 Improvements". Reading Borough Council. http://www.reading.gov.uk/ltp/General.asp?id=SX9452-A7832CD2. 
  15. ↑ "Reading is the fastest-growing economic centre in UK". Reading Chronicle. 10 July 2007. http://icberkshire.icnetwork.co.uk/chronicle/headlines/tm_headline=reading-is-the-fastest-growing-economic-centre-in-uk&method=full&objectid=19433560&siteid=50102-name_page.html. 
  16. ↑ M4 VICKERS MACHINE GUN PILLBOX, PILLBOX STUDY GROUP
  17. ↑ New speed limit on part of M4, South Wales Argus Saturday 4 April 2009
  18. ↑ www.m4widening29to32.com
  19. ↑ "Council will look again at case for M-way link". icwales. 23 June 2007. http://icwales.icnetwork.co.uk/news/cardiff-news/2007/06/23/council-will-look-again-at-case-for-m-way-link-91466-19345314/. 
  20. ↑ "Business park plan ‘would hit green land’". icwales. 19 December 2007. http://icwales.icnetwork.co.uk/business-in-wales/business-news/2007/12/19/business-park-plan-would-hit-green-land-91466-20266885/. 
  21. ↑ "Plans for the M4 Toll (Newport)". BBC News. 20 September 2007. http://news.bbc.co.uk/2/hi/uk_news/wales/7003690.stm. Retrieved 12 May 2010. 
  22. ↑ "The New M4 Project – Magor to Castleton". Welsh Assembly Government. 13 July 2009. http://wales.gov.uk/publications/accessinfo/drnewhomepage/transportdrs2/transportdrs2009/m4projmagor-castleton/?lang=en. 
  23. ↑ "ARE M4 PLANS ON RIGHT TRACK?". South Wales Evening Post. 12 December 2007. http://www.thisissouthwales.co.uk/displayNode.jsp?nodeId=161818&command=displayContent&sourceNode=161644&contentPK=19049034&folderPk=88499&pNodeId=161375. 
  24. ↑ Area 3 Driver Location Signs (map) - Highway Authority, 2009
  25. ↑ Driver Location Signs, M5 J18-11, M4 J22-15 (map) Highway Authority 2009
  26. ↑ "Traffic England Live Traffic Condition Map (selected Popups)". Highways Agency. http://www.trafficengland.com/map.aspx. Retrieved 2009-11-05. 

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