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.
Latest active roadworks on the M4
Roadworks live on the M4 right now.
M4 Westbound Jct 4B exit slip road lane 1 closure
01:2017 Sept 2026reported 51 min ago
- Location
- link road from M4 J4B westbound to M25 J15
- Direction
- Westbound
- Lanes closed
- Slip road closed
- Reason
- Roadworks
- Schedule
- 22:00 Wed 16 Sept 2026 → 05:30 Thu 17 Sept 2026
+ 4 more active roadworks - search all M4 traffic news →
Latest planned roadworks on the M4
The next planned roadworks scheduled on the M4.
M4 eastbound lane 1 and 2 closure (100/8 to 98/2)
01:2017 Sept 2026reported 51 min ago
- Location
- M4 eastbound between J14 and J13
- Direction
- Eastbound
- Lanes closed
- Lane closures
- Reason
- Repair work
- Schedule
- 20:00 Thu 17 Sept 2026 → 06:00 Fri 18 Sept 2026
Forecast - not confirmed
+ 11 more planned roadworks - search all M4 traffic news →
Road closed — on the overhead signs now
National Highways’ overhead signs are showing a road closure, as at 02:12 Thu 17 Sept 2026. 5 other serious messages are on the signs - see them all below.
M4 J21 - J23 CLOSED
Time now: Thursday, 17 September 2026, 02:1201:1217 Sept 2026set 59 min ago✓ Checked by us 02:12
M4 J21 - J23
CLOSEDOverhead Message
WhereM4 westbound, at J19 · on 1 signAlso onAlso showing on M5 signsSinceOn the signs since at least 22:35 Wed 16 Sept 2026We check these overhead signs at least every five minutes, but we can't guarantee a sign is still current if an incident or issue has been cleared and the sign has not been updated yet. Signs and news can each carry something the other does not - check both before you travel.
Search all the latest M4 traffic news →
Updated 02:12 Thu 17 Sept 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.