Major British interchanges

[Burwellian]

I guess, but M11 J13 (A1303) completes a fair few of them.

[jackal]

BUMP

I was wondering if there are any new interchanges (i.e. opened since 2008) that meet the above criteria. I can't think of any offhand but probably I am forgetting a couple. (The M1/A46 upgrade isn't far off but the roundabout to the South breaks the mainline.). There are also one or two like M62/M57 that have had substantial upgrades.

[paully]

The A889/A705 cloverleaf (Livingston) doesn't meet the criteria imho as the A705 doesn't even have a central reservation - it's only a single carriageway. Although the criteria states "no break in the central reservation" (which is strictly true as there isn't one to break) I don't see how a fairly minor junction with a local access road is a "major British interchange".

[jackal]

The A889/A705 cloverleaf (Livingston) doesn't meet the criteria imho as the A705 doesn't even have a central reservation - it's only a single carriageway. Although the criteria states "no break in the central reservation" (which is strictly true as there isn't one to break) I don't see how a fairly minor junction with a local access road is a "major British interchange".

I agree, I've added a dual carriageway requirement and removed the offending junction. I also removed M53/A552 and A386/B3413 as they do not have continuous DC on their mainlines. This leaves the Redditch cloverleaf as the only one included on the list.

[Sam]

I might have just missed it, but I couldn't see A1/M62 in the list - definitely one of the more interesting freeflow junctions constructed in the last few years. Indeed, I've wondered whether there will ever be any more as grand... :-/

[jackal]

I might have just missed it, but I couldn't see A1/M62 in the list - definitely one of the more interesting freeflow junctions constructed in the last few years. Indeed, I've wondered whether there will ever be any more as grand... :-/

It's certainly a very nice junction but it is not full access, hence not on the list.

[Chris Bertram]

I might have just missed it, but I couldn't see A1/M62 in the list - definitely one of the more interesting freeflow junctions constructed in the last few years. Indeed, I've wondered whether there will ever be any more as grand... :-/

It's certainly a very nice junction but it is not full access, hence not on the list.

True, there is one set of movements (A1(M)S to M62E and reverse) that is catered for by the A162 and the old 3-level stacked r/bout junction with the services.

[RichardA626]

The A889/A705 cloverleaf (Livingston) doesn't meet the criteria imho as the A705 doesn't even have a central reservation - it's only a single carriageway. Although the criteria states "no break in the central reservation" (which is strictly true as there isn't one to break) I don't see how a fairly minor junction with a local access road is a "major British interchange".

What's the story behind this cloverleaf & the other in Livingston?

Also did Headless Cross need a cloverleaf?

[Sam]

I might have just missed it, but I couldn't see A1/M62 in the list - definitely one of the more interesting freeflow junctions constructed in the last few years. Indeed, I've wondered whether there will ever be any more as grand... :-/

It's certainly a very nice junction but it is not full access, hence not on the list.

Ah of course - and I wouldn't suggest stretching the junction to include the old A1/M62 stacked roundabout.

[paully]

What's the story behind this cloverleaf & the other in Livingston?

Tha A705 (Cousland Rd) and Houston Rd (the road which was met by the removed cloverleaf) were both built with the intention of being dualled , you'll notice they both have grade-separated junctions to the West of the A899, and have room under all the bridges for a second carriageway. The second carriageway was never built, and to be honest was probably never needed.

[wrinkly]

When current works are completed, M74/A725 will qualify.

If and when current plans are built, A19/A1058 will qualify.

[jackal]

When current works are completed, M74/A725 will qualify.

If and when current plans are built, A19/A1058 will qualify.

I think the most recent junction on the list is M40/A34, opened in Autumn 2004. So by my estimate the UK will have gone more than 12 years without building a qualifying junction when M74/A725 opens. England will have gone 14 years when A19/A1058 opens.

To put this in context, prior to 2005 there had been on average one qualifying junction completed every year...

[jackal]

BUMP since I thought it worth noting that at least four of the junctions already on the list were scheduled for major upgrades in the RIS. Wisley (M25/A3) is due for 'improvement ... to allow free-flowing movement in all directions' and M42/A45 (does this have a name?) is due for a 'comprehensive upgrade', with construction to start by 2020 on both. By 2025 Lofthouse is due for 'reconstruction ... as an all-direction free-flowing interchange' and Simister Island is due for a less specific 'comprehensive improvement'. Other stackabouts like M25/A12 are getting smaller improvements.

[Chris Bertram]

M42/A45 (does this have a name?)

Middle Bickenhill is the nearest named settlement, but I've never heard it called that.

[ais523]

We call it Bickenhill Interchange on our wiki. The name doesn't really seem to be in use elsewhere, though (a web search on the term mostly finds people complaining about the naming of the nearby proposed HS2 junction, normally as a kind-of gotcha "well it's actually in Bickenhill").

From my point of view as a pedestrian, it's effectively part of Hampton-in-Arden, the only settlement that has decent pedestrian links to and from the junction.

[Glenn A]

Greymoorhill, or jct 44 of the M6 near Carlisle, this has seen a big increase in traffic since the NDR was built and now has plenty of east-west traffic avoiding Carlisle using it. Not surprisingly the junction has been upgraded with more traffic lights at the roundabout as it has traffic travelling to Edinburgh and Glasgow, the Scottish Borders, Carlisle city centre, west Cumbria and the North East. I don't think it's as busy as jct 40 at Penrith, though.

[jackal]

A slightly different aspect - from the original list and subsequent discussion, it appears that the UK probably has no more than 50 major grade-separated DC/M'way interchanges. Am I the only one who thinks that's a rather paltry number for a country with a population of about 60 million?

On a per capita basis, yes, it is rather paltry. However, I think it is rather generous in relation to centerline miles--Britain has just 2,000 miles of motorway plus (rough estimate) an additional 1,000-2,000 miles of comprehensively grade separated dual carriageway for which it is appropriate to provide system interchanges. Of course, a rather higher density of elaborate interchanges is necessary to service a driving population of about 26 million (compared to about 200 million in the USA, with an Interstate network of circa 45,000 miles supplemented by perhaps 10,000 additional miles of state and US route freeway).

Anyone hazard a guess what the totals would be for e.g. France, Germany or Italy? Obviously Germany rules when it comes to the cloverleaf but apart from that I don't really have much of a feel for this.

It's hard to speak in terms of numbers without doing a count. My impression is that system interchanges are dense in the Netherlands and Belgium and rather less so in France, Spain, and Italy. Because so many of the long-distance comprehensively grade-separated routes in the latter three countries are toll highways, the proportion of system interchanges that are freeflow is lower, and there is a correspondingly higher fraction of double trumpets and the like.

In terms of four-level stack interchanges (deliberately restricting this category to interchanges with a Maltese cross configuration), Britain has more (3) than any other European country. Other European countries with stacks include Germany (1), Greece (at least 1), Spain (at least 1), and the Netherlands (at least 1). The USA has at least 53, in Texas (at least 25), California (9), Michigan (4), Arizona (3), Ohio (3), Alabama (3), Maryland (1, with another currently under construction), Florida (at least 1), New York (at least 1), Washington (1), Louisiana (1), and Tennessee (1).

However, interchange configuration is not the only determinant of high capacity. In order to realize the full capacity advantages of a particular design, you need to provide geometry that is as generous as practicable. It is theoretically possible, for example, to build a four-level stack which handles various movements less efficiently than some cloverleaf designs. The left-turning direct connectors in the original Four Level have curve radii which are not significantly larger than those used for the loop ramps in some cloverleaf interchanges.

I have, years later, compiled some data on this. Here's a comparison of four-way freeflow interchange totals in various European countries:

United Kingdom 13 (3 stack, 4 turbine, 1 one loop, 3 cloverstack, 2 cloverleaf)
Austria 10 (3 cloverstack, 1 2 loop adjacent, 2 cloverleaf, 4 offside)
Lithuania 9 (8 cloverleaf, 1 offside)
Sweden 8 (1 cloverstack, 1 2 loop adjacent, 1 3 loop, 4 cloverleaf, 1 offside)
Latvia 6 (4 cloverleaf, 1 other nearside, 1 offside)
Denmark 4 (1 3 loop, 3 cloverleaf)
Luxembourg 3 (1 cloverstack, 1 2 loop adjacent, 1 other nearside)
Moldova 2 (2 cloverleaf)
Albania, Bosnia, Estonia, Georgia, Iceland 1 (1 cloverleaf)

And here is the number of four-way full access freeflow interchanges per million population:

Luxembourg 5.34
Lithuania 3.13
Latvia 3.04
Iceland 3.01
Austria 1.15
Estonia 0.76
Sweden 0.81
Denmark 0.70
Moldova 0.69
Albania 0.35
Bosnia 0.29
Georgia 0.27
United Kingdom 0.20

So yes, the UK has very few four-way full freeflow interchanges on a per capita basis.

I think it would fair somewhat better if we factor in stackabouts and other non-freeflow designs on the 'major british interchange' list - that gets it to about 0.78 per million. I don't have numbers for stackabouts etc in other countries, but I think there are very few, so the UK would probably be around the same level as Denmark or Sweden. Of course, a better comparison would be with a country with a similar population, like Italy or France, which I hope to do in time.

More detail on methodology etc here.

[Chris_533976]

BUMP since I thought it worth noting that at least four of the junctions already on the list were scheduled for major upgrades in the RIS. Wisley (M25/A3) is due for 'improvement ... to allow free-flowing movement in all directions' and M42/A45 (does this have a name?) is due for a 'comprehensive upgrade', with construction to start by 2020 on both. By 2025 Lofthouse is due for 'reconstruction ... as an all-direction free-flowing interchange' and Simister Island is due for a less specific 'comprehensive improvement'. Other stackabouts like M25/A12 are getting smaller improvements.

Wisley is absolutely absurd the way it is. The M25 and the A3 joined up with a three level stack.... without even freeflow slips.

It won't get it, but would it deserve a 4-stack or is that overkill?

[jackal]

BUMP since I thought it worth noting that at least four of the junctions already on the list were scheduled for major upgrades in the RIS. Wisley (M25/A3) is due for 'improvement ... to allow free-flowing movement in all directions' and M42/A45 (does this have a name?) is due for a 'comprehensive upgrade', with construction to start by 2020 on both. By 2025 Lofthouse is due for 'reconstruction ... as an all-direction free-flowing interchange' and Simister Island is due for a less specific 'comprehensive improvement'. Other stackabouts like M25/A12 are getting smaller improvements.

Wisley is absolutely absurd the way it is. The M25 and the A3 joined up with a three level stack.... without even freeflow slips.

It won't get it, but would it deserve a 4-stack or is that overkill?

The latest AADT counts there are:

175975 M25 West
152040 M25 East
87861 A3 South
81682 A3 North

These suggest that there will be very high turning volumes, and I think three of the four movements probably require semi-direct or cyclic connectors. A loop for M25 westbound to A3 northbound might be okay though.

DMRB at least used to suggest an upgrade path for stackabouts that involved adding two cyclic connectors, with two more cyclic connectors replacing the roundabout in a second stage, with a full turbine as the final arrangement. Of course, this was only a suggestion, and there are many other ways to fully freeflow a stacked roundabout, including adding semi-direct connectors in stages until you have a full stack.

[Peter Freeman]

... and there are many other ways to fully freeflow a stacked roundabout, including adding semi-direct connectors in stages until you have a full stack.

I'd like to see most stackabouts eventually eliminated and I like the idea of gradually reaching full freeflow in stages, but isn't this pathway a wasteful one, leaving you with four unused bridges?