M40 - A43
You are here: Home » Bad Junctions » M40-A43
Ordnance Survey map Alternative aerial view
Where is it?
M40 junction 10, where the A43 splits off towards Northampton. This is one of the waypoints on the main freight route from Southampton to the north east.
What's wrong with it?
When the A43 between the M40 and M1 was upgraded to dual carriageway recently, this junction was updated too. It was built in 1991 as a regular two-roundabout dumbbell junction, but the improvements produced this. Amongst other things, it takes up more land than the previous junction, makes access in almost any direction difficult, and marginalises the most popular movement between M40 south and the A43. The previous set of four straight sliproads have been replaced by five sharply curved, narrow ones.
But what is most shocking about this junction is that at the northernmost roundabout, traffic from the A43 onto the M40 crosses traffic from the M40 north to the A43 - leaving north-eastbound traffic queuing northbound around two roundabouts and back onto the M40 northbound carriageway, even outside busy periods. It's such a stunningly shortsighted and dangerous mistake that it leaves me completely lost for words to describe how awful this new layout is.
Why is it wrong?
Well, here's the thing: it's hard to see any justification whatsoever for this layout. It's not smoother, it's not an improvement in width or speed of sliproads (in fact, lorries are now prone to tipping over on the sliproads), it doesn't make access to the services any easier... it makes, in short, no positive changes at all to the junction. How on earth did this design make it off the drawing board?
What would be better?
The most immediate solution would be to block the northernmost entry slip road to the M40 southbound, so A43 traffic no longer crosses at the northern roundabout. This would prevent almost all of the congestion at this junction. After that, I don't know. Maybe we could hunt down whoever designed this shameful mess.
Update: traffic lights have now been installed - no, not on the whole junction, just on the approach from the A43 south-westbound. Presumably when traffic gets bad enough northbound, these will act as 'ramp metering' - allowing bursts of traffic off the A43 southbound, creating gaps in the flow that will give northbound traffic a chance to get through.
There is also a new 50mph limit applying to the whole junction. This will make things much safer as one of the major problems it suffers is people tearing round those three queue-free roundabouts at dangerously high speeds.
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.
Nick Wedd is confused:
I am puzzled by the layout of this junction. Who thought that the present curious layout, with two slip roads both providing access to the M40 southbound, was an improvement over what was there before? And why?
Richard has seen the light:
I'm in favour of the traffic lights on the approach on the A43.
Some time before they were installed, I was on my way from Oxford to Northampton, and having heard of an accident that had closed the M40 at this junction, I travelled north on the B430.
However, it was the southbound M40 that was closed one junction further north, so there was no traffic leaving the motorway at this junction. That gave the A43 southbound traffic free access to the roundabout, as there was no traffic to give way to. Consequently, both M40 and B430 northbound on to the A43 joined forces at the M40 northbound exit roundabout, and was faced with the traffic leaving the A43 to join M40 south, where it had right of way.
Took me two hours to drive the six miles up the B430 that day.
Loving the lights.
David has seen the answer:
The only improvement I can see with the new layout is that A43 to M40 (northbound) traffic no longer conflicts with M40 (northbound) to A43 traffic - but is that really an issue? Certainly not a big enough one to rebuild an entire junction, I would submit.
Surely the solution to most of the problems here is obvious - connect the south-most of the 2 southbound on-slips to the roundabout, and not just the service area. Then close the curved southbound on-slip to the north. That immediately removes the main traffic conflict.
If you're feeling really energetic, re-instate the straight off-slip as well, which means you can remove the northern of the 3 roundabouts and keep the curved off-slip as a diverge for A43-bound traffic only. If that were topped off with a new off-slip for the services sited south of the junction, you remove the other major traffic conflict. The sad thing is that the fire at the services gave the HA and the Services operator a good chance to do something useful - but did they?
I can see the pigs soaring high above me on any of the above happening...
Duncan Stewart is stirred into action:
Now the lights have been installed on the southbound A43 the junction is much worse. Not only does Northampton-bound traffic exiting the M40 queue, but now at peak times the southbound does too, all the way back to RAF Croughton some 2-3 miles away! Why don't we all just get together and hire some diggers to re-open the old southbound slip road?! I hate this junction...
Andrew Taylor isn't keen on the new lights:
I notice you have updated the page to reflect recent developments, but these haven't helped a great deal. The junction was closed again [a few weeks later] after yet another HGV fell over negotiating the roundabouts.
