How Busy Is M4 Junction 5 to 6?
Between Junction 5 at Langley and Junction 6 for Slough and Windsor, the M4 runs along the southern edge of Slough, one of the busiest parts of the motorway west of London.
In the Department for Transport’s 2025 traffic counts it carried 138,753 vehicles a day, making it the third busiest of the 47 stretches between numbered junctions on the M4 that we could compare. This stretch has 3 count points; the figures here are from the busiest one.
Live traffic speed flow: M4 Junctions 4 to 7
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Latest M4 traffic news
Live traffic news at M4 Junctions 5 and 6
This is the news for Junctions 5 and 6 only, not the whole M4. For the rest of the motorway see all the latest M4 traffic news, the overhead signs and the speed limits in force now.
Updated 02:57 (2:57am) Sun 1 Nov 2026
For everything currently reported on the M4, see our latest M4 traffic news, M4 roadworks and M4 accidents.
Traffic on M4 Junction 5 to 6
138,753 vehicles a day works out at an average of about 5,781 an hour, or roughly 96 a minute, around the clock. That average takes in quiet nights as well as busy rush hours, so at peak times the flow is much heavier.
Split by direction, that count point measured 69,511 vehicles a day eastbound and 69,241 westbound.
Cars and taxis make up about 78% of the traffic. Vans account for around 16%, about 21,702 a day, and lorries for 8,436 a day, 6.1% of everything on the road.
The junctions at each end
Junction 5 (A4) serves Langley, east Slough and Datchet. Junction 6 (A355) serves central Slough, Windsor and Eton. Every junction on the motorway, with the service areas in between, is on our map of the M4 junctions, and the places to stop are listed on M4 services.
How it compares with the rest of the M4
The busiest stretches of the M4 are almost all at the London end, between Hayes and Slough, where airport, London and M25 traffic meet. The table shows the ten busiest.
| 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.