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

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These are the most recent comments on this junction. You can see all comments if you prefer.

September 2011

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.

March 2011

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.

March 2011

Jon is dicing with death:

I moved to Almondsbury about 4 months ago and I travel all over the South West for work and this is still the worst part of any journey.

People who use only the M5/M4 think this is bad, try going Northbound from the A38 and attempt to get onto the M5 on any morning when the M4 is jammed down to the M32. Whilst the junction is awful, the thoughtless and horrendous driving tendancies by impatient drivers coming off the M5(N) to join the M4 Eastbound make this junction an absolute death-trap. To get onto the M5 Northbound you have to effectively cross a single file queue of traffic trying to get onto the M4E distributor road, so whilst you cross that first line of traffic to get into clear air for the M5, you will get some idiot come flying down the outside trying to tuck into the M4E collector lane at the last minute and thus taking me or someone else out!!!

The only suggestion I can think of is that M5 traffic should have a separate way to join the A38 at Junction 16 and let the M4 traffic flow freely into either the A38 or the M5.

January 2011

Matt has big ideas:

A lot of traffic should be removed from this junction all together by building a new motorway east of Bristol, this could connect with the mystery junction on the M4 between Bath and the M32. It could continue north to meet the M5 closer to Michaelwood Services and south to meet the M5 near Clevedon. Any traffic heading to and from London could then miss this busy junction all together.

The M49 does a similar job for traffic travelling between the South West and Wales and I imagine it contributes massively to reducing congestion at Almondsbury (apart from the silly roundabout junction where it meets the M4 - Doh!)

November 2010

David Unwin puts it in context:

Part of the problem was that the M5 between now junctions 16 and 17 was built as a small bypass of Filton and predates the Almondsbury interchange.

It is akin to the M60 junctions 11 to 13 situation where the local junctions 11 and 13 were part of the original Stretford - Eccles bypass and predate the major interchange at junction 12 (M60, M62, M602, former M63) which had to be shoehorned in afterwards and the existing bypass widened.