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M4 MOTORWAY
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The M4 motorway is a motorway in England and Wales linking London and west Wales via Bristol. Other major places directly accessible from M4 junctions are Reading, Swindon, Newport, Cardiff and Swansea.
Notes
In the construction of the section around Cardiff in 1980, 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 2005, 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 the 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".
Special features
The M4 has several special features. In London, the eastbound (London-bound) carriageway has a bus lane from junction 3 until the elevated section. This lane caused much controversy when it was created. However, the bus lane has (counterintuitively) improved traffic flow onto the 2-lane elevated section which follows it; there is some evidence that the original plan simply involved closing one lane from J3 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 J3 because the left lane at J3 is exclusively for traffic leaving the motorway, so the effect of the bus lane is to make the 3-to-2 transition seamless). Making the "spare" lane available for buses - and now taxis - was an afterthought.
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.
25 miles (40 km) west, 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.
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). (The London Orbital M25 motorway requires the use of the toll-collecting Dartford Crossing to complete a circuit, but the crossing itself is downgraded to an "A" road to allow use by local traffic).
There is a slip road west of the A34 to Newbury from the eastbound carriageway which leads to RAF Welford. This slip road is marked by a red and white roadsign.
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.[1]
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.
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).
Junctions
| M4 Motorway |
| Eastbound |
Junction |
Westbound |
| London A4 |
1 |
Start of motorway |
| A4 North Circular A406 South Circular A205 Chiswick A315 |
2 |
Brentford A4 |
| Heston services |
| Heathrow Terminal 4 & Cargo, Hayes, Harrow, Hounslow A312 |
3 |
Heathrow Terminal 4 & Cargo, Hayes, Harrow, Feltham A312 |
| Heathrow Terminals 1, 2 & 3 (A4) Uxbridge (A408) |
4 |
Heathrow Terminals 1, 2 & 3 (A4) Uxbridge (A408) |
| Heathrow Terminal 4 & Cargo, Gatwick Airport, Watford, Oxford M25 |
4B |
Heathrow Terminal 4 & Cargo, Gatwick Airport, Watford, Oxford M25 |
| Colnbrook, Langley A4 Eton, Datchet B470 |
5 |
Colnbrook, Langley A4 Datchet B470 |
| Slough A355 Windsor A322 |
6 |
Slough A355 Windsor A322 |
| Slough (A4) |
7 |
Slough (A4) |
| High Wycombe, Henley A404(M) Maidenhead A308(M) |
8/9 |
High Wycombe, Henley A404(M) Maidenhead A308(M) |
| Reading, Wokingham, Bracknell A329(M) |
10 |
Reading, Wokingham, Bracknell A329(M) |
| Basingstoke, Reading, A33 |
11 |
Basingstoke, Reading, A33 |
| Reading services |
| Reading, Theale A4 |
12 |
Reading, Theale A4 |
| Newbury, Oxford A34 & Chieveley services |
13 |
Newbury, Oxford A34 & Chieveley services |
| Hungerford, Wantage A338 |
14 |
Hungerford, Wantage A338 |
| Membury services |
| Swindon A419 Marlborough A346Oxford (A420) |
15 |
Swindon, Gloucester A419Marlborough A346 |
| Swindon A3102 |
16 |
Swindon A3102 |
| Chippenham A350 Cirencester A429 |
17 |
Chippenham A350 Cirencester A429 |
| Leigh Delamere services |
| Bath, Stroud A46 |
18 |
Bath, Stroud A46 |
| Bristol M32 |
19 |
Bristol M32 |
| The SOUTH WEST, Bristol, The MIDLANDS, Gloucester M5 (Almondsbury Interchange) |
20 |
The SOUTH WEST, Bristol, Exeter, The MIDLANDS, Gloucester M5 (Almondsbury Interchange) |
| No exit |
21 |
Chepstow M48 |
| Avonmouth M49 The SOUTH WEST, Bridgwater, Exeter (M5) |
22 |
Avonmouth M49 |
| Second Severn Crossing |
| Chepstow M48 |
23 |
No exit |
| Magor, Caldicot B4245 & Magor services |
23A |
Magor, Caldicot B4245 & Magor services |
| City centre A48, Newport B4237, Monmouth A449, The MIDLANDS (M50) |
24 |
City centre A48, Newport B4237, Monmouth A449 |
| No exit |
25 |
Caerleon B4596 |
| No exit |
25A |
Newport, Cwmbran A4042 |
| Brynglas Tunnels |
| Newport, Cwmbran, Caerleon A4051 |
26 |
Newport A4051 |
| High Cross B4591 |
27 |
High Cross B4591 |
| Newport A48 Risca, Brynmawr A467 |
28 |
Newport A48 Risca, Brynmawr A467 |
| No exit |
29 |
Cardiff A48(M) |
| Cardiff A4232 |
30 |
Cardiff A4232 |
| Cardiff, Merthyr Tydfil A470 |
32 |
Cardiff, Merthyr Tydfil A470 |
| Cardiff & Airport, Barry, Penarth A4232 & Cardiff West services |
33 |
Cardiff & Airport, Barry, Penarth A4232 & Cardiff West services |
| Llantrisant, Rhondda A4119 |
34 |
Llantrisant, Rhondda A4119 |
| Pen-coed A473 |
35 |
Bridgend, Pen-coed A473 |
| Bridgend A4061 Maesteg A4063 & Sarn Park services |
36 |
Bridgend A4061 Maesteg A4063 & Sarn Park services |
| Porthcawl, Pyle A4229 |
37 |
Porthcawl, Pyle A4229 |
| Port Talbot A48 |
38 |
Port Talbot A48 |
| No exit |
39 |
No exit |
| Port Talbot A4107 |
40 |
Port Talbot A4107 |
| Port Talbot A48 |
41 |
Briton Ferry A48 |
| Swansea A483 Briton Ferry A48 |
42 |
Swansea A483 |
| Neath, Merthyr Tydfil A465 |
43 |
Neath, Merthyr Tydfil A465 |
| Swansea A48 |
44 |
Swansea A48 |
| Swansea, Pontardawe A4067 |
45 |
Swansea, Pontardawe A4067 |
| Swansea B4489 |
46 |
Swansea B4489 |
| Swansea A483 & Swansea West services |
47 |
Swansea A483 Pontarddulais A48 & Swansea West services |
| Pontarddulais, Llanelli A4138 |
48 |
Pontarddulais, Llanelli A4138 |
| Start of motorway |
49 |
Carmarthen A48 Ammanford A483 & Pont Abraham services |
See also
References
- ^ "Drivers hold M4 speed camera demo", BBC News, April 30, 2005.
External links
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