M4 - M5 - A38

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Where is it?

Junction diagramNorth 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

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.

May 2016

ER disagrees:

I just don't see the problem with this junction. It's fine whenever I use it!

May 2016

Martin Jonez can't see:

Coming from Wales on the M4 and joining the M5 southbound is so dangerous as you arrive blind on a flyover bend in the outside lane of the M4 joining the M5 south. If you are driving a lorry you cannot see in the left mirror what's coming. Even more dangerous if you survive the flyover and then want to come off on the A38.

May 2015

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.

February 2015

Anonymous 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.

January 2015

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!?