M40 - A404
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Ordnance Survey map Alternative aerial view
Where is it?
M40 junction 4. The major M40 junction for the large town of High Wycombe and connection point with the A404, a major dual carriageway route connecting it with Maidenhead and the M4.
What's wrong with it?
It simply can't cope. The usual trick of adding traffic lights has - surprise surprise - not done an awful lot to help. The major flow of traffic is between the A404 to the south and M40 to the west, meaning the most popular movements are bogged down by stop lines all the way around.
Actually, since this page was created, the Highways Agency have made a substantial improvement by creating a dedicated right-turn through the middle of the roundabout for M40 eastbound to A404 southbound traffic, and installed a free-flowing sliproad for the reverse movement. It's not as good as a free-flowing solution, and many of the junction's problems remain, but it's a start...
Why is it wrong?
It wasn't meant to be a major junction. It was always intended to be a busy junction, serving three routes north into High Wycombe, but the A404 has been upgraded bit by bit until now it is a clear alternative to the M25. Since the M25 between the M40 and M4 is heavily congested day and night, the A404 takes lots of traffic, and this terminal junction simply can't cope.
What would be better?
The option that has been installed to improve it is a cut-across to bypass the three northern exits, so traffic exiting the M40 eastbound zips across and joins the other side of the roundabout quickly. This was tried at the Stansted exit on the M11 where much the same problem was encountered, and it didn't work. Stansted now has free-flow slip roads. Let's get the same built here.
Right to reply
Hate this junction? Or do you think it hasn't had a fair trial? Make yourself heard! Post a comment.
These are the most recent comments on this junction. You can see all comments if you prefer.
Michael1952 thinks big:
The grid-locks are often as not caused by drivers jumping the lights subsequently blocking entrances as they wait to enter their exit. I would propose that the WHOLE round about is made into a box junction supported by appropriately placed (and sign posted!) box junction cameras.
For a signalised roundabout to work, there have to be places where traffic queues on the roundabout itself, so making the whole thing a box junction would need some serious remodelling! -Ed.
Geoff is struck by inspiration:
Perhaps a magic roundabout like junction one would have been better.
An anonymous contributor writes:
My main gripe with his junction is with the drivers that don't understand the lane rules as you exit the junction for the southbound A404. All three lanes can be used for entering the A404, but ONLY the left hand lane is for turning left towards Marlow Bottom. So many drivers cut across from the middle lane turning left towards Marlow Bottom. One day they will be T-boned by a car going straight across.
Charles got some information on what the HA are planning next. They wrote:
"In the longer term we will link the signals to the Reading Control Room so that we can remotely monitor and change the timings to suit traffic conditions. This remote control was always intended but we have had problems with a telephone link."
So what's the latest? Has this Bad Junction redeemed itself? -Ed.
Alex Lakey is frustrated by the same problem:
I emailed the DfT last night after spending 90 mins to go 700 yards up the A404, around the roundabout and join the eastbound M40.
I have known this roundabout for years, and although the old design was pretty hideous, the new junction has new issues, as described in my email below:
"The problem is basically that there is no protection of the exit junctions and crossing points from the inner loop and roundabout to the surrounding connected roads, hence when the roundabout becomes busy the traffic reaches a point when the entire roundabout becomes a solid loop.
"I cannot see why there cannot be box junctions (monitored by cameras) to protect the major exits on the roundabout and control the waves of traffic allowed onto the roundabout. Although these would obviously be an extra cost, the box junction painting in itself would cause most drivers to think again before blocking the roundabout exits, and would be significantly cheaper than any changes to the light phasing or additional roadworks."
See all 10 comments about this junction »
With thanks to Chris and Paul Baker for information on this page.
