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
E-mail me with your comments.
Robin adds:
I've watched this junction 'grow' from when it was a temporary end of the M40. The A4010 is to blame, being a 'bypass'. Plans were made to move the whole M40/A404 junction south, but this has now been superceded by a plan to burrow the A4010 through the roundabout to the southbound A404 to avoid conflict with the M40. I think we shall be seeing even more traffic lights!
Howard Cox writes:
Surely the fact that the M40 is reduced to two lanes at this point just for the duration of the junction has something to do with the chaos. The M40 was originally all two lane, then slowly turned into permenant roadworks to increase width to three and even four lanes - super - except for this 200-yard section which simply hasn't got the room without a complete rebuild of the whole junction and bridge.
Ian writes:
Is the fact that the M40 is down to two lanes through the junction, often resulting in long queues, ever going to be sorted? There would seem to be enough room if the hard shoulder is 'lost' through the bridges, as happens in some places elsewhere where widening has taken place, eg M25 j9 to 8.
David Plato is pleased:
The work that is mentioned is now complete. A hige slipway now cuts across the roundabout, bypassing the A4010, the road to the north and the A404 north. It's a lot easier to get from the A404 from Maidenhead onto the M40 towards London.
A new slipway now goes from the A404 from Maidenhead, under the road to Marlow bottom and then onto the M40 towards Birmingham. In short, traffic from the A404 can now be routed onto the M40 (both directions) much easier.
Craig Wilson isn't quite so happy: (Apr 08)
Unfortunately, since this junction has been completed, it regularly goes into gridlock. Lorries coming off the M40 south heading onto the A404 via the new roundabout block the traffic from flowing around, allowing only a few cars through the lights at a time. The junction needs yellow boxes painted onto it, or a complete re-build... But let's face it, they would probably make it even worse again.
Alex Lakey is frustrated by the same problem: (Apr 08)
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."
Charles got some information on what the HA are planning next. They wrote: (Apr 08)
"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 yet?
With thanks to Chris and Paul Baker for information on this page.
