M40 - A43
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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 The previous set of four straight sliproads have been replaced by five sharply curved, narrow ones.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
David Griffiths adds:
None of the usual excuses for bad junctions is applicable here - I am absolutely mystified by it. The only reason I can think of is that it was completely rushed so that the Silverstone access improvements were completed quickly enough to keep Bernie Ecclestone happy.
Chris Bertram comments:
It's even worse than your diagram indicates, as the slip from the middle roundabout to the M40 south is only accessible from the services, and not from the main roundabout, so B430 traffic wanting to go south must do the dance round three roundabouts to get there. When they were reconstructing the junction, I happily imagined that they'd seen sense and were installing some sort of free-flowing trumpet-based affair, but no! Damn right it's worse than before, the only possible justification is that the roads are wider so possibly higher capacity, but fatally compromised by the movement conflicts.
Andy Taylor writes:
My opinion of it is going from bad to worse. Today the junction was closed due to an overturned HGV on one of the small roundabouts. This is not the first time this has happened since it opened. A proper free-flowing junction which could have been constructed at similar cost would have prevented these problems.
Anonymous adds:
I could not believe the revised access from the A43 to the M40 when I first used it. I thought it must be a temporary measure, and a bad one at that! No-one surely would design a system that has southbound traffic (A43E-M40S) crossing the eastbound (M40S-A43E), would they? I can vouch for the fact that, no matter what time of day, queuing extends back over two roundabouts. I hate to think what it must be like when it is busy! When it comes to your turn, the sight of heavy lorries hurtling round the conflicting roundabout (A43E-M40S) makes you shudder as they lean to the reverse exit curve. In short, total amateurism!
Peter Risebrow adds:
I agree with everything you say about this awful junction - the main problem, of course, being the ludicrous crossing-over of easbound and westbound traffic. However, having been round this junction for the first time recently, I think there is a slight mistake in your drawing. It looks from your drawing as if you can join the M40 Southbound from the A43 Westbound in one of two ways (ie "straight over" at the first roundabout, or turn left at the first roundabout, then down the slip road off the second roundabout) This is not possible (as I found out the hard way) as the slip road onto the M40 comes directly out of the Services, not off the roundabout!
Stewart Moody writes:
As a regular west London to Lancashire commuter I can vouch for everything you say about this ridiculous junction layout. At peak times the tailback of traffic moving north along the A43 backs down onto the M40 northbound lane 1 for approximately 1000 mtrs. Let's have a round of applause for the design team!
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.
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...
And that's quite enough comments now, thank you! I think we all get the idea that this is a very poor junction layout...
With thanks to Andrew, Des Howlett, Roger Cantwell and Graham Coleman for information on this page.
