How Busy Are the M4 Junctions?
The M4 runs from west London to Pont Abraham in west Wales, and the traffic along it varies enormously. If you use the same junctions every week, how busy your own stretch is matters far more than an average for the whole road. These pages take the M4 one stretch at a time, using the Department for Transport’s 2025 traffic counts, with the latest news alongside.
The busiest stretch, J4 to J4b, carried 156,491 vehicles a day. The quietest, at the far western end between J48 and J49, carried 50,421, roughly a third as many.
Latest M4 traffic news
Search all the latest M4 traffic news
Latest accident or incident on the M4
The most recent accident or incident on the M4 that we are aware of.
M4 westbound at junction J15: overturned vehicle
00:10 (12:10am)1 Nov 2026reported 3 hr ago
- Location
- M4 westbound at junction J15
- Direction
- Westbound
- Lanes closed
- There are two of three lanes closed. The hard shoulder, lanes one and two are closed
- Reason
- Overturned vehicle
- Schedule
- 23:55 (11:55pm) Sat 31 Oct 2026 → 01:00 (1am) Sun 1 Nov 2026
Latest active roadworks on the M4
Roadworks live on the M4 right now.
Hardshoulder closure
02:56 (2:56am)1 Nov 2026reported just now
- Location
- M4 eastbound between J17 and J16
- Direction
- Eastbound
- Lanes closed
- Hard shoulder closed
- Reason
- Roadworks
- Schedule
- 23:59 (11:59pm) Tue 27 Apr 2021 → 18:00 (6pm) Fri 30 July 2027
Latest planned roadworks on the M4
The next planned roadworks scheduled on the M4.
M4 eastbound Jct 19 to Jct 18 hard shoulder running 174/6-170/5
02:56 (2:56am)1 Nov 2026reported just now
- Location
- M4 eastbound between J19 and J18
- Direction
- Eastbound
- Lanes closed
- Hard shoulder closed
- Reason
- Roadworks
- Schedule
- 20:00 (8pm) Sat 31 Oct 2026 → 06:00 (6am) Sun 1 Nov 2026
Forecast - not confirmed
Search all the latest M4 traffic news
Updated 02:57 (2:57am) Sun 1 Nov 2026
Powered by National Highways’ Transport Data Feeds.
Everything currently reported is on our latest M4 traffic news page.
M4 junction pages
M4 Junction 4 to 4b: Heathrow
156,491 vehicles a day, the busiest stretch of the M4.
M4 Junction 4b to 5: The M25 to Langley
140,828 vehicles a day, the second busiest stretch of the M4.
M4 Junction 5 to 6: Slough
138,753 vehicles a day, the third busiest stretch of the M4.
M4 Junction 3 to 4: Hayes and Heathrow
136,321 vehicles a day, the fourth busiest stretch of the M4.
M4 Junction 8/9 to 10: Maidenhead to Winnersh
115,951 vehicles a day, the eleventh busiest stretch of the M4. Closed after a serious collision on 9 and 10 September 2026.
M4 Junction 10 to 11: Winnersh to Reading
121,922 vehicles a day, the eighth busiest stretch of the M4. Closed all weekend 18 to 21 September 2026 for power line work.
Why the London end is so busy
The four busiest stretches of the M4 are all between Hayes and Slough. Traffic to and from Heathrow Airport, traffic heading in and out of London, and traffic joining or leaving the M25 at Junction 4b all use the same few miles of motorway.
The ten busiest stretches of the M4
| Rank | M4 stretch | Vehicles per day | Lorries |
|---|---|---|---|
| 1 | J4 to J4b | 156,491 | 6,249 |
| 2 | J4b to J5 | 140,828 | 8,712 |
| 3 | J5 to J6 | 138,753 | 8,436 |
| 4 | J3 to J4 | 136,321 | 5,243 |
| 5 | J19 to J20 | 128,594 | 11,167 |
| 6 | J6 to J7 | 127,570 | 7,577 |
| 7 | J7 to J8/9 | 126,197 | 7,861 |
| 8 | J10 to J11 | 121,922 | 8,549 |
| 9 | J28 to J29 | 121,902 | 9,572 |
| 10 | J25 to J25a | 117,507 | 9,599 |
Traffic figures are annual average daily flows, both directions together, from the Department for Transport road traffic statistics for 2025. On the M4 many stretches are split into more than one count point; where a stretch has more than one, the busiest measured point is shown. The ranking covers 47 stretches between numbered junctions; slip roads, spurs and the complex junctions 41 to 43 are left out. Hourly and per-minute figures are simple averages across the whole day and night. Contains public sector information licensed under the Open Government Licence v3.0.