The A404(M) is a spur from the M4 to the A4 and A404 running to the west of Maidenhead, but it was once the main road to Bristol and the west, and is now on its third road number.

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, weirdly numbered to echo the two junctions it replaced. This little spur motorway is what was left behind, the old end of the M4 travelling to White Waltham and Maidenhead Thicket. Meanwhile, junction 8/9 has now existed for decades longer than junctions 8 and 9 ever did.

This short section of road is a strange time machine, 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 early-1960s charms, the A404(M) offers 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 were sacrificed in the 1970s to create a third running lane.

When it first gained its own identity, 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, with the old one crossed out, but it's been the A404(M) for about 30 years.

Despite looking and sometimes feeling like a museum piece, the A404(M) remains busy, serving a very useful purpose, and is still a trunk road. In fact it's more useful now than it ever was, linking to the A404, which continues as a fast dual carriageway route north to Handy Cross. Together they make a very well-used connection between the M4 and the M40 and carry significant amounts of traffic that would otherwise clog up Reading or the M25.


Maidenhead Thicket





Connects to

2 miles

Click a section name to see its full details, or click a map symbol on the right to see all motorways opened in that year.

Completed Name Start End Original number Other numbers
Maidenhead Bypass M4 J8/9 Holyport J9B The Thicket M4 A423(M) Chronology map for 1961

Exit list

Symbols and conventions are explained in the key to exit lists. You can click any junction to see its full details.

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

A404 (M40)

LanesLanesLanesLanes Signs LanesLanesLanesLanes Signs
1 mile, 2 lanes 1 mile, 2 lanes
46.2 km
Cox Green
White Waltham
Cox Green
White Waltham
LanesLanesLanesLanes LanesLanesLanesLanes
1 mile, 2 lanes 1 mile, 2 lanes
M4 J8/9
45.2 km
N/A M4



A308(M) Link
Heathrow Airport
M4 Link
M4 Link
LanesLanesLanesLanes LanesLanesLanesLanes

Picture credits

With thanks to Peter Harris, Tim Lidbetter and James Broadway for information on this page.

In this section

What's new

London’s other forgotten motorways

We’ve spent years documenting the unbuilt urban motorway network planned for London. Today we’re unveiling more new routes that have never been seen before!

The middle of nowhere

A national system of road numbers radiating from a central point suggests there is… well, a central point. But if you go looking for it you’ll find it doesn’t exist.

Not so Smart

There have been rumours for months. Now the announcement has been made - “all new Smart Motorways scrapped”. What does this mean and who are the winners?

Share this page

Have you seen...

Aust to Beachley

Today two motorways cross the Severn near Chepstow. But as recently as 1965, the only crossing was a ferry that carried six cars at a time, from Aust to Beachley.

About this page


Last updated