M4 motorway
|
mile
|
km
|
Eastbound exits (B carriageway)
|
Junction
|
Westbound exits (A carriageway)
|
7.3
|
11.8
|
Road continues asA4toCentral London
|
J1 [coord 1]
|
Start of motorway
|
8.3 8.5
|
13.4 13.7
|
North CircularA406 South CircularA205 ChiswickA315
|
J2
|
Staines,Hounslow,BrentfordA4
|
12.5 12.8
|
20.1 20.6
|
Heston services
|
Services
|
Heston services
|
13.4 13.7
|
21.5 22.1
|
Heathrow (Terminals4,5& Cargo),Hayes,Harrow,HounslowA312
|
J3
|
Heathrow (Terminals4,5& Cargo), Hayes, Harrow, Hounslow A312
|
15.2 15.7
|
24.5 25.2
|
Heathrow (Terminals2&3) (A4) Uxbridge A408
|
J4a
|
Heathrow (Terminals2&3)(A4) UxbridgeA408
|
16.8 17.7
|
27.0 28.5
|
Heathrow(Terminals4,5& Cargo) ,Gatwick Airport ,Watford(M3),(M23),(M40),(M1)M25
|
J4b [coord 2]
|
Heathrow (Terminals 4, 5&Cargo), Gatwick, Watford (M3), (M23), (M40), (M1), M25
|
19.1 19.5
|
30.7 31.4
|
Colnbrook,Langley,Slough (East)A4 Eton,DatchetB470
|
J5
|
Colnbrook,Langley,Slough (East)A4,DatchetB470
|
22.9 23.2
|
36.8 37.4
|
Slough (Central)A355 WindsorA322
|
J6
|
Slough (Central)A355 WindsorA322
|
24.7 25.0
|
39.8 40.3
|
Slough (West)A4
|
J7
|
Slough (West)A4
|
27.8 28.2
|
44.7 45.4
|
High Wycombe,HenleyA404(M) MaidenheadA308(M)
|
J8/9
|
High Wycombe,HenleyA404(M) MaidenheadA308(M)
|
35.0 35.8
|
56.4 57.6
|
Reading (East),Wokingham,BracknellA329(M)
|
J10
|
Reading (East),Wokingham,BracknellA329(M)
|
40.6 41.2
|
65.4 66.3
|
Basingstoke,Reading (Central & South)A33
|
J11
|
Basingstoke,Reading (Central & South)A33
|
43.5 43.8
|
70.0 70.5
|
Reading services
|
Services
|
Reading services
|
45.3 45.7
|
72.9 73.5
|
Reading (West),ThealeA4
|
J12
|
Reading (West),ThealeA4
|
56.9 57.2
|
91.5 92.1
|
Newbury,OxfordA34 Chieveley services(Moto)
|
J13 Services [coord 3]
|
Newbury,OxfordA34 Chieveley services(Moto)
|
64.4 64.8
|
103.7 104.3
|
Hungerford,WantageA338
|
J14
|
Hungerford,WantageA338
|
68.7
|
110.5
|
Membury services
|
Services
|
Membury services
|
76.4 77.1
|
122.9 124.0
|
Swindon(East)A419 MarlboroughA346 Oxford(A420)
|
J15
|
SwindonA419,MarlboroughA346
|
82.4 82.8
|
132.6 133.2
|
Swindon(West),Royal Wootton Bassett,Wroughton,MoD Lyneham,CalneA3102
|
J16
|
Swindon (West),Royal Wootton Bassett,Wroughton,MoD Lyneham,CalneA3102
|
94.8 95.3
|
152.5 153.4
|
ChippenhamA350 CirencesterA429
|
J17
|
ChippenhamA350 CirencesterA429
|
96.7
|
155.7
|
Leigh Delamere services
|
Services
|
Leigh Delamere services
|
104.9 105.6
|
168.8 170.0
|
Bath,StroudA46
|
J18
|
Bath,StroudA46
|
112.8 113.2
|
181.5 182.1
|
Bristol M32
|
J19
|
BristolM32
|
115.8 116.3
|
186.3 187.2
|
The SOUTH WEST,Bristol(West),The MIDLANDS,Gloucester,Bristol Airport ,M5
|
J20 Almondsbury Interchange [coord 4]
|
The SOUTH WEST, Bristol (West) M5(S) The MIDLANDS, Gloucester M5(N)
|
117.7 189.5
|
189.5 190.0
|
No access
|
J21
|
ChepstowM48
|
121.3 121.6
|
195.2 195.7
|
AvonmouthM49
|
J22
|
Avonmouth M49
|
121.7 124.1
|
195.9 199.8
|
Entry into England
|
Second Severn Crossing [coord 5]
|
Entry into Wales
|
127.0
|
204.4
|
No toll plaza
|
Bridge Toll
|
Former Toll plaza (closed Dec 2018)
|
129.2
|
208.0
|
ChepstowM48
|
J23
|
No access
|
131.4 132.2
|
211.4 212.8
|
Magor,CaldicotA4810 Magor services
|
J23A Services
|
Magor,CaldicotA4810 Magor services
|
134.8 135.6
|
217.0 218.3
|
City centreA48 Newport(East)B4237 MonmouthA449 The MIDLANDS(M50)
|
J24
|
City centreA48 Newport(East)B4237 MonmouthA449
|
137.9
|
222.0
|
No access
|
J25
|
CaerleonB4596
|
138.3
|
222.6
|
No access
|
J25A
|
Newport,CwmbranA4042
|
138.8 139.1
|
223.4 223.8
|
Brynglas Tunnels
|
Tunnel
|
Brynglas Tunnels
|
139.1 139.5
|
223.8 224.5
|
Newport,Cwmbran,CaerleonA4051
|
J26
|
NewportA4051
|
140.8 141,4
|
226.6 227.6
|
High CrossB4591
|
J27
|
High CrossB4591
|
142.0 142.9
|
228.5 230.0
|
NewportA48 Risca,BrynmawrA467
|
J28
|
NewportA48 Risca,BrynmawrA467
|
143.6
|
231.1
|
No access
|
J29
|
Cardiff(East and South)A48(M)
|
146.6 147.3
|
236.0 237.0
|
Cardiff (East)A4232 Cardiff Gate services
|
J30 Services
|
Cardiff (East)A4232 Cardiff Gate services
|
151.9 244.5
|
244.5 246.1
|
Merthyr Tydfil,CardiffA470
|
J32
|
Cardiff (North),Merthyr TydfilA470
|
155.4 156.0
|
250.1 251.1
|
Cardiff (West),Barry,PenarthA4232 Cardiff Airport![](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/20_airtransportation.svg/15px-20_airtransportation.svg.png) Cardiff West services
|
J33 Services
|
Cardiff (West),Barry,PenarthA4232 Cardiff Airport![](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/20_airtransportation.svg/15px-20_airtransportation.svg.png) Cardiff West services
|
157.5 158.1
|
253.5 254.4
|
Llantrisant,RhonddaA4119 Royal Glamorgan Hospital
|
J34
|
Llantrisant,RhonddaA4119 Royal Glamorgan Hospital
|
163.9 164.4
|
263.7 264.5
|
Pen-coedA473
|
J35
|
Bridgend,Pen-coedA473
|
167.5 168.3
|
269.6 270.8
|
BridgendA4061 MaestegA4063 Princess of Wales Hospital Sarn Park services
|
J36 Services
|
BridgendA4061 MaestegA4063 Princess of Wales Hospital Sarn Park services
|
172.8 173.5
|
278.1 279.3
|
Pyle,PorthcawlA4229
|
J37
|
Porthcawl,PyleA4229
|
177.0 177.3
|
284.9 285.3
|
Port TalbotA48
|
J38
|
Port TalbotA48
|
178.3
|
286.9
|
No access (on-ramp only)
|
J39
|
No access
|
179.7 179.9
|
289.2 289.6
|
Port TalbotA4107
|
J40
|
Port TalbotA4107
|
180.9 181.3
|
291.1 291.8
|
Port TalbotA48
|
J41
|
Briton FerryA48
|
183.9 184.9
|
295.9 297.3
|
Briton FerryA48 Swansea (South)A483
|
J42
|
Swansea (South)A483
|
184.9 185.7
|
297.5 298.8
|
Neath,Merthyr TydfilA465
|
J43
|
Neath,Merthyr TydfilA465
|
187.0 187.4
|
300.9 301.6
|
Swansea (East)A48
|
J44
|
Swansea (East)A48
|
188.8 189.3
|
303.9 304.7
|
Pontardawe,Swansea (North)A4067
|
J45
|
Pontardawe,Swansea (North)A4067
|
190.8 191.4
|
307.0 308.0
|
LlangyfelachB4489 Felindre Morriston Hospital
|
J46
|
LlangyfelachB4489 Felindre Morriston Hospital
|
192.4 193.1
|
309.6 310.7
|
Swansea (West)A483 GorseinonA48 Swansea services
|
J47 Services
|
Swansea (West)A483 GorseinonA48 Swansea services
|
196.4 197.1
|
316.0 317.2
|
Pontarddulais,LlanelliA4138
|
J48
|
Pontarddulais,LlanelliA4138
|
199.2
|
320.6
|
Start of motorway
|
J49 Terminus Services [coord 6]
|
Motorway terminates at a roundabout: CarmarthenA48 Ammanford,LlandeiloA483 Pontarddulais A48 Pont Abraham services
|
1.000 mi = 1.609 km; 1.000 km = 0.621 mi
|