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Route of the A404(M)

The A404(M) — along with its little brother the A308(M) — has the dubious honour of starting at Britain's only double-numbered junction: M4 junction 8/9. The story goes that when the M4 was first built, it ran as far as Maidenhead. Junction 8 was present day 8/9 and junction 9 was at the top end of what is now the A404(M). When it was extended further west, it branched off at junction 8, not 9, and the little spur left over became A404(M). So that motorists weren't confused junction 8 became 8/9. Which is far less confusing, apparently, even though 8/9 has now been in existence much longer than the original 8 and 9.

Among its quaint, early-60s charms, the A404(M) features some toe-curlingly tight corners at junction 9A and the examples of bridges and other structures on the M4 with hard shoulders complete, unlike the widened sections of the M4 to the east. The exception is for the southernmost section towards J8/9, which was built in 1971 to connect the old road to the new roundabout.

Despite looking and feeling like another M45-style empty and bypassed early motorway, the A404(M) continues to serve a useful purpose — it's part of a very well-used connection between the M4 and junction 8/9 and the M40 at junction 4.

Between being the M4 and the A404(M), this road was the A423(M) — the number it has held the longest in total.


Start Stud Green (M4, A308(M))
Finish Woolley Green (A404)
Passes Maidenhead
Length 2 miles
Connects to M4, A308(M)


Views of the A404(M) from on and off the road. If you have a photo to contribute, contact me.


Southbound on the A404, and we approach the A4 junction and the start of motorway restrictions. In the early 1990s this roundabout interchange was built to replace the flat roundabout that terminated the original M4 bypass.
Photo by Dave Ryan


The sign at 9A warns of the perils ahead for anyone going to Cox Green. The road itself is another quiet, well-preserved early motorway.
Photo by Dave Ryan


Here's the southbound exit at 9a itself - with an advisory 30mph limit. It also looks like this deceleration lane has been extended by removing the hard shoulder - what it must have been like originally is anyone's guess.
Photo by Dave Ryan

Construction Timeline

When the various parts of the A404(M) were built, listed in chronological order.

Open Jct Section
May1961 Entire motorway Former M4

Exit List

All the junctions and destinations along the route.

Junction   Northbound               Southbound
48.8 km
High Wycombe
Oxford (M40 Link)

A404 (M40)
Maidenhead Thicket (Roundabout Interchange)

N/A More information about this junction
LanesLanesLanesLanesSigns LanesLanesLanesLanesSigns
1 mile, 2 lanes Up   Down 1 mile, 2 lanes
46.2 km
Cox Green
White Waltham
(Non-standard interchange) Cox Green
White Waltham
More information about this junction
LanesLanesLanesLanes LanesLanesLanesLanes
1 mile, 2 lanes Up   Down 1 mile, 2 lanes
(M4 J8/9)
45.2 km
N/A M4

M4 Junction 8/9 (Roundabout Interchange)


A308(M) Link
Heathrow Airport
M4 Link
M4 Link
More information about this junction
LanesLanesLanesLanes LanesLanesLanesLanes

With thanks to Peter Harris, Tim Lidbetter and James Broadway for information in this section.