Why does the UK not have any D2+1 roads?

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ajuk
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Why does the UK not have any D2+1 roads?

Post by ajuk »

Seems like a good idea for long distance roads that are important but not too busy, just make them slightly wider, put a fence down the middle and have the third lane that alternates the overtaking lane every mile, a bit like the Ilminster bypass, but a lot longer and with a partition so the limit is 70.
Al__S
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Re: Why does the UK not have any D2+1 roads?

Post by Al__S »

how much, realistically, does that save over a D2?
Herned
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Re: Why does the UK not have any D2+1 roads?

Post by Herned »

They are a bit of a niche thing, I know Scandinavian countries use them where distances are long and volumes relatively low. In Sweden they are often retrofitted from wide S2 roads, much like the Ilminster bypass, rather than built from new.

They also have the disadvantage that if something breaks down on the 1 side, the road is blocked. As Al says, they can't be much cheaper than just building D2
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KeithW
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

Well there is an example in Wales on the A477 here
https://www.google.co.uk/maps/@51.73264 ... 8192?hl=en

There are also 3 lane roads where the solid white alternates, the Louth bypass is one example. This is not some old S3 road from the 50's of 60's it was built in the late 1980's
https://www.google.co.uk/maps/@53.35379 ... 8192?hl=en

I have seen similar layouts elsewhere in Wales and Scotland as well as parts of the USA, they are basically climbing lanes in most cases.
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Re: Why does the UK not have any D2+1 roads?

Post by Glen »

We have WS2+1, which is a relatively recent design standard, which has the same purpose, but without a central reservation.
Its purpose is to provide guaranteed overtaking opportunities to break up platoons of traffic on long distance routes, so is normally provided with overtaking provision in both directions; which differs from the intention of traditional climbing lane layouts.

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From the SABRE Wiki: WS2+1 :

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Re: Why does the UK not have any D2+1 roads?

Post by Bryn666 »

Glen wrote: Thu Jan 06, 2022 10:12 We have WS2+1, which is a relatively recent design standard, which has the same purpose, but without a central reservation.
Its purpose is to provide guaranteed overtaking opportunities to break up platoons of traffic on long distance routes, so is normally provided with overtaking provision in both directions; which differs from the intention of traditional climbing lane layouts.

Image
This is the best compromise as this allows you to get past a broken down vehicle - Keith's A477 example has had to provide a hatched out area for the same purpose which means you've built a D2 by default.
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Re: Why does the UK not have any D2+1 roads?

Post by Fenlander »

The easiest way to upgrade parts of the A17/A16/A47 and no doubt many other roads round here would be with the odd bit of S2+1. It doesn't need to be Motorway, it doesn't even need to be dual carriageway, just give us the odd bit of clear road to get past the slower stuff safely.
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Re: Why does the UK not have any D2+1 roads?

Post by Herned »

KeithW wrote: Thu Jan 06, 2022 08:58 Well there is an example in Wales on the A477 here
https://www.google.co.uk/maps/@51.73264 ... 8192?hl=en
I bet that was built as D2 though and the lane removed later
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Vierwielen
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Re: Why does the UK not have any D2+1 roads?

Post by Vierwielen »

Possibly the UK authorities are happy to allow more congestion to occur before they react at which time they need to build a full D2 road.
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KeithW
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

Herned wrote: Thu Jan 06, 2022 11:12
KeithW wrote: Thu Jan 06, 2022 08:58 Well there is an example in Wales on the A477 here
https://www.google.co.uk/maps/@51.73264 ... 8192?hl=en
I bet that was built as D2 though and the lane removed later
I don't think so, according to the wiki the Kilgetty and Stepaside bypass was only opened in 1984 with less than half a mile of it being D2. The main reason for not being D2 seems to have been the cost of digging the cutting.
https://www.sabre-roads.org.uk/wiki/ind ... title=A477

From the SABRE Wiki: A477 :


The A477 provides the link from A40 at St Clears to the holiday venues on the Pembroke peninsula and the ferry port of Pembroke Dock (this part being part of the Trans European Road Network linking Europe to Ireland). It then connects the Pembroke peninsula to the area north of the Milford Haven estuary via the Cleddau Bridge which opened in 1975. The route prior to the bridge required either a ferry crossing to Neyland or a 40-mile detour

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KeithW
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

Fenlander wrote: Thu Jan 06, 2022 11:11 The easiest way to upgrade parts of the A17/A16/A47 and no doubt many other roads round here would be with the odd bit of S2+1. It doesn't need to be Motorway, it doesn't even need to be dual carriageway, just give us the odd bit of clear road to get past the slower stuff safely.
Adding a couple of Wide S2 sections to the A19 between Thirsk and York certainly helped a lot, to the extent that Talivans are now a frequent sight :)
https://www.google.co.uk/maps/@54.11872 ... 8192?hl=en
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Re: Why does the UK not have any D2+1 roads?

Post by M4Simon »

Herned wrote: Thu Jan 06, 2022 11:12
KeithW wrote: Thu Jan 06, 2022 08:58 Well there is an example in Wales on the A477 here
https://www.google.co.uk/maps/@51.73264 ... 8192?hl=en
I bet that was built as D2 though and the lane removed later
I'm pretty sure it was built with the hatching. Spin the camera around (use the 2011 images so you can see it without the temporary barrier) and you'll see an arched bridge with the start of a left turn lane underneath it. The edge of that lane is very close to the cutting face. If it had been built with two lanes, the cutting would have needed to be wider to accommodate the left turn lane, the bridge span longer, and the scheme more expensive.

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Re: Why does the UK not have any D2+1 roads?

Post by Herned »

KeithW wrote: Thu Jan 06, 2022 12:13 I don't think so, according to the wiki the Kilgetty and Stepaside bypass was only opened in 1984 with less than half a mile of it being D2. The main reason for not being D2 seems to have been the cost of digging the cutting.
https://www.sabre-roads.org.uk/wiki/ind ... title=A477
So if there was a section of D2, where is it?

From the SABRE Wiki: A477 :


The A477 provides the link from A40 at St Clears to the holiday venues on the Pembroke peninsula and the ferry port of Pembroke Dock (this part being part of the Trans European Road Network linking Europe to Ireland). It then connects the Pembroke peninsula to the area north of the Milford Haven estuary via the Cleddau Bridge which opened in 1975. The route prior to the bridge required either a ferry crossing to Neyland or a 40-mile detour

... Read More
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ajuk
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Re: Why does the UK not have any D2+1 roads?

Post by ajuk »

Al__S wrote: Thu Jan 06, 2022 06:57 how much, realistically, does that save over a D2?
Well considering how difficult it was to upgrade the A465 from high standard S2+1 to D2, I think it some cases quite a lot.
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Re: Why does the UK not have any D2+1 roads?

Post by jnty »

Thinking about WS2+1 vs. D2+1 raises a question - what is it about central barriers that makes a (quieter, country) road safer? How much of it is that overtaking into the opposite carriageway is prevented and how much of it is cars which 'drift' for whatever reason (crash, inattention, impairment) are physically barred from the other side? The former certainly feels like it would be more common on these roads than the latter. I'm trying to get a sense for how much the UK is 'compromising' by avoiding the barrier given that it feels like almost all wrong-side overtakes can be avoided with frequent WS2+1 plus average speed cameras if necessary.

I can imagine that WS2+1 is a bit nicer for cyclists on the 1 side, although presumably continental schemes might be more likely to include separate NMU provision throughout.
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Re: Why does the UK not have any D2+1 roads?

Post by skiddaw05 »

jnty wrote: Thu Jan 06, 2022 12:53 Thinking about WS2+1 vs. D2+1 raises a question - what is it about central barriers that makes a (quieter, country) road safer?
I've sometimes wondered this about that even rarer beast, the rural S4
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

Herned wrote: Thu Jan 06, 2022 12:44
KeithW wrote: Thu Jan 06, 2022 12:13 I don't think so, according to the wiki the Kilgetty and Stepaside bypass was only opened in 1984 with less than half a mile of it being D2. The main reason for not being D2 seems to have been the cost of digging the cutting.
https://www.sabre-roads.org.uk/wiki/ind ... title=A477
So if there was a section of D2, where is it?

Good question - take it up with whoever wrote the wiki entry. My guess was that it was here where one carriageway has been marked down to 1 lane.
https://www.google.co.uk/maps/@51.73037 ... 8192?hl=en

From the SABRE Wiki: A477 :


The A477 provides the link from A40 at St Clears to the holiday venues on the Pembroke peninsula and the ferry port of Pembroke Dock (this part being part of the Trans European Road Network linking Europe to Ireland). It then connects the Pembroke peninsula to the area north of the Milford Haven estuary via the Cleddau Bridge which opened in 1975. The route prior to the bridge required either a ferry crossing to Neyland or a 40-mile detour

... Read More
jnty
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Re: Why does the UK not have any D2+1 roads?

Post by jnty »

skiddaw05 wrote: Thu Jan 06, 2022 13:11
jnty wrote: Thu Jan 06, 2022 12:53 Thinking about WS2+1 vs. D2+1 raises a question - what is it about central barriers that makes a (quieter, country) road safer?
I've sometimes wondered this about that even rarer beast, the rural S4
I suppose rural S4s probably end up in a 'survival of the unfittest' situation - the ones wide enough to provide a reasonable level of safety will be relatively easy to upgrade to D2, and the ones that aren't will stick around and look unsafe (and probably get changed to something else as well.) I don't know of any NSL rural S4s but I'd imagine they're on roads so quiet that safety's not a huge consideration. I'm not sure any cost savings for "WS4" vs. D2 "from scratch" would ever be worth it.

There's also the fact that it's two overtaking vehicles likely to be meeting at the centre line which are likely to both be going faster, especially if it's quite a short section, I suppose.
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Re: Why does the UK not have any D2+1 roads?

Post by Herned »

So is it:
KeithW wrote: Thu Jan 06, 2022 14:24 The main reason for not being D2 seems to have been the cost of digging the cutting.
or
KeithW wrote: Thu Jan 06, 2022 14:24 Good question - take it up with whoever wrote the wiki entry. My guess was that it was here where one carriageway has been marked down to 1 lane.
As your replies seem very contradictory.

I would guess that entire section including the junction was built as D2 and then later, probably after some nasty accidents, it was rebuilt the way it is today
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Re: Why does the UK not have any D2+1 roads?

Post by A320Driver »

Going by the nomenclature in another recent thread, shouldn’t it be D1+1? I.e. dual, one-lane carriageways, one of which has an extra lane?
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