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Route of the A404(M)

The A404(M) is a spur from the M4 to the A4 and A404 running to the west of Maidenhead. Along with its little brother the A308(M), it has the dubious honour of starting at Britain's only double-numbered junction, M4 junction 8/9.

This little spur started life as the end of the M4. Travelling west from London, the thrilling new motorway ran as far as Maidenhead, turning north and dropping traffic back onto the old A4 at Maidenhead Thicket. Junction 8 connected to the A308 and junction 9 was the local interchange at White Waltham. When the M4 was extended further west, towards Reading, it branched off its old route at what is now junction 8/9, leaving behind a little spur to White Waltham and Maidenhead Thicket. Junction 8/9 has now existed for longer than junctions 8 and 9 ever did.

What's left behind is a short section of road that is barely modified from the days when it was part of the M4, offering a snapshot of what this major route looked like when its first sections opened. Among its quaint, early-60s charms, the A404(M) features some toe-curlingly tight corners on the sliproads at junction 9A, and bridges and other structures with hard shoulders complete, unlike the widened sections of the M4 to the east where they have been sacrificed to create a third running lane.

When it was first bypassed, the spur was given the number A423(M), in recognition of it connecting to the A423 at Maidenhead Thicket. The A423 was then absorbed into the A404, and the junction at Maidenhead Thicket gained an underpass, at which point the motorway was renumbered A404(M). There are still a couple of signs on and around the spur indicating the change to its "new" number.

Despite looking and sometimes feeling like an empty museum piece, the A404(M) continues to serve a very useful purpose and is still a trunk road. Together with the A404, which continues north to Handy Cross, it's part of a very well-used connection between the M4 and the M40 and carries significant amounts of traffic that would otherwise clog up Reading or the M25.


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 Formerly 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.