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
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.
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.
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."
"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."
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.
Perhaps a magic roundabout like junction one would have been better.
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.
I hope that whoever had the entertaining idea of putting a chicane in the M40 at this junction gets stuck in the customary five-mile London-bound tailback one Sunday evening with three hysterical small children and a full bladder.
The junction is a victim of piecemeal addition of routes, a failure to plan in advance to create capacity for greater traffic volumes, and being hemmed in on the north side of the junction. Originally the junction only had one north-south route (Marlow Rd into Marlow Bottom Road). Now there are three routes coming in at the north side of the roundabout (A404 Marlow Hill and A4010 John Hall Way).
Also the development of the Marlow Bypass and subsequently the A404(M) has meant a free-flowing grade separated junction should be built between the M40 and the Marlow Bypass. However because of the ASDA supermarket, cinema and hotel, there isn't enough room to create an effective grade separated junction between the Marlow Bypass and the M40.
The fudge of the inside route for M40E to Marlow Bypass and vice-versa traffic is better than nothing, but this will never be anything other than a pinch point (and source of misery for commuters) unless the commercial properties north west of the junction are cleared.
Also the confusing lane system often leads drivers trying to get to the A4010 trying to join from the middle lane on the roundabout (either barging in aggressively to avoid the orderly queue, or those genuinely confused by the layout).
If knocking it down and starting from scratch were an option, I'm sure the planners would take it!
I can still remember my parents having to use this junction simply to turn around having visited the leisure centre just to the NE of the junction, as the only way you can leave the car park is in the direction of this junction. That was in the 80's, and it was hellish then.
The improvements that have been made between the A404 and the M40 do appear to have assisted slightly, but the crux of the issue is that there are simply too many roads coming together. It might make sense to remove the northernmost access to the roundabout, as that housing estate has access elsewhere. It would also assist if it were possible for traffic from High Wycombe town centre to gain access to the newish retail park to the NW of the junction without having to use the junction! Keep motorway access traffic and local traffic apart.
Around 1993 a scheme was developed to realign the motorway and build a new interchange well to the south of the existing junction. It was accepted at that time that there was nothing clever that could be done with the existing junction. The scheme was dropped in a round of transport budget cuts.