M4 - M5 - A38
Where is it?
North of Bristol, the point where two of the most important roads in South West England cross each other and, rather ambitiously, attempt to interact with the local road network at the same time. This is actually two junctions on the M5 that are stuck together — junction 15 for the M4 and junction 16 for the A38 at Filton.
It is one of the most-nominated Bad Junctions ever.
What's wrong with it?
In its component parts, nothing at all. It took me years to work up the courage to actually list this on the site because junction 15, the M4-M5 interchange, is a four level stack, one of the highest capacity junctions it is possible to build and one of only three of its type in the UK. We could do with far more of them, so it feels quite wrong to see it here.
The Maltese Cross at Almondsbury isn't the problem (though the motorways it connects could do with a bit of extra capacity). The trouble is that it has been glued on to another hapless junction with the A38, a major road into Bristol and now surrounded by shops, offices and car parks.
Linking the two overloaded junctions is a collector-distributor road setup that collects traffic for a brief scramble to change lanes before splitting up into sliproads for the next junction.
Why is it wrong?
In 1966, the year it opened, Almondsbury was the most incredibly complex and exciting junction the UK's road network had ever seen. It had a free-flowing interchange with four levels! It had four motorway carriageways running parallel to each other! It had it all.
Unfortunately what happened to Almondsbury is traffic. When there's not many people on the roads, all that lane changing on the outer linking carriageways is easy. Once it starts to get busy you have problems: traffic coming from the M4 westbound has to move right and right again on its way to the M5 southbound, while trying not to bang in to the M5 southbound traffic frantically moving left to reach the A38. The more vehicles there are, the harder it is to maneouvre, and the more everyone is in everyone else's lane.
The worst bit is that all of the roads here are predisposed to come to a shuddering halt in the summer when the holiday traffic is passing through, and any sort of traffic jam blocking those collector-distributor lanes will then spread onto all the surrounding sliproads and make the perilous lane-changing moves even more dangerous than before. Changing from a lane travelling at speed into a stationary one is not an easy trick to pull off.
What would be better?
This interchange is crying out for some investment. It was once the marvel of the motorway network and it doesn't deserve its bad reputation. I feel quite sorry for it.
The most obvious improvement is to get rid of those outer collector-distributor carriageways, and replace them with a braided junction. Separate sliproads would cross each other with flyovers to carry conflicting traffic movements without incident.
Right to reply
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These are the most recent comments on this junction. You can see all comments if you prefer.
OldNick Has an update:
The interchange is at the moment getting a particularly bad name for itself, after an unidentified body has changed the phasing on the traffic lights at the J16 A38 roundabout. This is resulting in morning tailbacks across the collector-distributor road setup, with considerable hazard to lfe, limb, and vehicle. And in the evening, drivers struggle to leave Bristol via this route.
An anonymous contributor missed their exit:
I was once traveling along the M5 northward, and was going to change to the M4 east at this junction. A lorry blocked the M4 exit, by pulling across (without indicating, I hasten to add) 2 lanes, and we had to go up to the next junction, and perform a u-turn.
What I would do is split the 4-lane M5 into 2 2-lane carriageways south of the A38. From the outer lane, a third lane would go to the A38, and then the sliproad from the A38 would split, one lane going to the main M5, the other joining the M5-M4 sliproad. The junction would then remain unchanged. Eh volia! A simple, safe, and easy junction for everybody.
Kreg is not impressed:
My my what a mess, since the opening of the 'Managed Motorway' section here, back in the Spring of 2014, the junctions have become an even bigger horror! The Southbound J16 sliproad is now a mad tango of four lanes, with frantic drivers dashing about trying to understand and comprehend the mad and slap dash signage which adorns them from above. For a moment, one might mistake this slip road as part of the M25 or M62, a true nightmare. I question the effectiveness and validity of the recent 'improvements', especially when I regularly find myself fighting a battle with other road users at rush hour, made worse by the Northerner tourists in the summer, you'd think they don't understand the concept of a slip road! Oh my, will we ever see a real improvement to this travesty of a junction!?
RG has a cunning plan:
How about this?
Build a half diamond from the A38's bridge over M4 (the bridge is already wide enough for the job), with slip roads facing SE, running alongside but not joining M4E (a la A414/M1 junction), until they join the slips roads to and from the M5. Traffic from M5N wanting to reach J16 would only have to cross SW - S Wales traffic, but since M49 that is easy.
Then you can close off the existing access between J16 and M5N, allowing two lanes for the whole length of the sliproads between London and the SW. J16-M4 traffic is unaltered, but now has more time and less competition for space to negotiate the junction.
At the same time, ideally, the M5 should be upgraded to 4 lanes each way from J17 to J15 (splitting 2 for M4, 2 for M5), and the M4 likewise desperately needs a 4th lane all the way to J19 (it only narrows to 3 lanes for about a mile currently!).
Almondsbury residents would probably take the extra traffic through their village in exchange for safer access to the M5 and M4!
P.S. This scheme could also serve as a decent temporary diversion to create the space for grade separating M5N-J16 from M4-M5 traffic, if that ultimately proved necessary.
I'm not quite so convinced that the people of Almondsbury would agree with you! -Ed.
Richard Lampitt has the answer:
Fixing this junction would be extremely easy. As suggested, a braided junction would be the best answer.
The model I'd suggest for it is the M8-A720 junction - two slip roads go around the M8 junction to access the the A71.
Similarly, the south-facing sliproads from the M4 can be routed around the A38 junction.