A404(M)

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.

Start

Maidenhead Thicket

End

Holyport

Passes

Maidenhead

Connects to
Length

2 miles

Open Junctions Section
May 1961 Entire motorway Formerly M4.

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  
9B
48.8 km
Twyford
Reading
Maidenhead
A4
Marlow
High Wycombe
Oxford (M40 Link)
A404







A4
NORTH
A404 (M40)







A4
N/A
LanesLanesLanesLanes Signs LanesLanesLanesLanes Signs
1 mile, 2 lanes 1 mile, 2 lanes
9A
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











SOUTH
A308(M)

M4











Windsor
A308(M) Link
London
Slough
Heathrow Airport
M4 Link
The WEST
Reading
M4 Link
LanesLanesLanesLanes LanesLanesLanesLanes
Routes

Picture credits

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

In this section

What's new

Imperfectly Odd: Batheaston Bypass

It has viaducts, a tunnel and plenty of controversy, but the amazing Batheaston Bypass doesn’t really work. What went wrong?

South London's lost motorways

Completing the story of London's epic Ringways, we've just published the Southern Radials, five more motorways that never saw the light of day.

To the north east!

Two new additions to our collection of Opening Booklets take us to Darlington and Middlesbrough.

Share this page

Have you seen...

A Piece of History

The lowly and pathetic A6144(M) motorway was downgraded in May 2006. This is the story of the mission to rescue some memorabilia.

About this page

Published22 April 2017

Last updated20 January 2022