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

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

Post by nowster »

dereer wrote: Sun Jan 09, 2022 13:10 In addition, many drivers dangerously overtake very close to the end of the 2 lane section, causing many near misses.
This happens a lot on the A9 between Perth and Inverness where the D2 sections end.
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KeithW
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

dereer wrote: Sun Jan 09, 2022 13:10 I live near the D2+1 section of the N2 in Castleblayney and I feel that D2+1s are fundamentally flawed.
....
Factors like these are almost certainly reasons why D2+1 roads aren't really a thing in the UK, as they have major drawbacks and are usually not suitable for significant amounts of traffic.
True but not as flawed as the S3 roads that a number of them replaced. We had a thread on this some years ago.
viewtopic.php?t=28353
Glenn A
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Re: Why does the UK not have any D2+1 roads?

Post by Glenn A »

nowster wrote: Sun Jan 09, 2022 13:41
dereer wrote: Sun Jan 09, 2022 13:10 In addition, many drivers dangerously overtake very close to the end of the 2 lane section, causing many near misses.
This happens a lot on the A9 between Perth and Inverness where the D2 sections end.
The A66 is another candidate for people who overtake as the D2 runs out and almost hit traffic in the S2. More reason why sections of S2 between D2s should be replaced where possible and needed.
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Re: Why does the UK not have any D2+1 roads?

Post by jnty »

KeithW wrote: Sun Jan 09, 2022 14:05
dereer wrote: Sun Jan 09, 2022 13:10 I live near the D2+1 section of the N2 in Castleblayney and I feel that D2+1s are fundamentally flawed.
....
Factors like these are almost certainly reasons why D2+1 roads aren't really a thing in the UK, as they have major drawbacks and are usually not suitable for significant amounts of traffic.
True but not as flawed as the S3 roads that a number of them replaced. We had a thread on this some years ago.
viewtopic.php?t=28353
I guess the question here is the suitability of D2+1 as a conversion option from S3 vs. WS2 or S2+1. Everyone is probably agreed that S3 is probably the worst of all worlds. It sounds like the latter options are probably better in terms of cost and practicality, but maybe not safety?
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Re: Why does the UK not have any D2+1 roads?

Post by jnty »

dereer wrote: Sun Jan 09, 2022 13:10 I live near the D2+1 section of the N2 in Castleblayney and I feel that D2+1s are fundamentally flawed.
Looking at the 1-lane section in your streetview link, it feels like there's almost enough space for a broken down car to pull over into the shoulder and verge? I suppose if doesn't manage to pull over people wouldn't be so keen to undertake on that though.

Looking at the A9 dualling, which would probably be a prime candidate for D2+1, it seems like most new D2 sections are built with NMU provision alongside and a fairly generous verge. So there's quite a lot more land take involved as standard than just the extra lane.

I wonder if there's room for a D2+1 version with a generous verge separating an NMU path which could be used for broken down vehicles, and maybe even a normal carriageway width on the 1 side which let tractors pull right over to allow careful overtaking? The default presence of the NMU path also means that's less of an issue.

This could be discontinuous through difficult sections like bridges - allowing you to save on width from D2 where it matters most - while still giving a bit more resiliency on the 1 section.
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

jnty wrote: Mon Jan 10, 2022 11:16 I guess the question here is the suitability of D2+1 as a conversion option from S3 vs. WS2 or S2+1. Everyone is probably agreed that S3 is probably the worst of all worlds. It sounds like the latter options are probably better in terms of cost and practicality, but maybe not safety?
It depends on how it is done, S2+1 is not as good as D2 and the problem with WS2 is that people tend to drive in the middle of the lane rather than move left when someone wants to overtake.
PhilC
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Re: Why does the UK not have any D2+1 roads?

Post by PhilC »

These are a few examples of D2+1 roads I know, but none of them was designed that way. At some point one of the lanes was hatched over.

The A38 Droitwich bypass

https://goo.gl/maps/dX69Ev84SxhKU7VXA

The A4091 south of Tamworth

https://goo.gl/maps/2jDeNRFbn8VVjELQ8

The A24 south of Leatherhead

https://goo.gl/maps/afXTHZR3iu6kZszd8

There is a short stretch of S4 on the A259, near Brighton.

https://goo.gl/maps/DYJxTFyG94GR1Y4P8
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Re: Why does the UK not have any D2+1 roads?

Post by KeithW »

You can see the same on the old A19 Billingham bypass now just Wolviston Road
https://www.google.co.uk/maps/@54.61965 ... 8192?hl=en
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dereer
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Re: Why does the UK not have any D2+1 roads?

Post by dereer »

jnty wrote: Mon Jan 10, 2022 11:24
Looking at the 1-lane section in your streetview link, it feels like there's almost enough space for a broken down car to pull over into the shoulder and verge? I suppose if doesn't manage to pull over people wouldn't be so keen to undertake on that though.
I can see your point, and having a NMU path beside the road would do a lot to alleviate this issue. However, if a lorry broke down, it could still result in other lorries being unable to get past. This is especially true on bridges where it is unlikely that there would be a verge.
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BaggieBoy
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Re: Why does the UK not have any D2+1 roads?

Post by BaggieBoy »

The A287 has a very short stretch of dual carriageway that has 2 lanes towards Farnham but only 1 in the other direction. There is space for second lane but it is hatched off.

https://goo.gl/maps/41zH53j6XTU5RRBu9
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skiddaw05
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Re: Why does the UK not have any D2+1 roads?

Post by skiddaw05 »

The narrowed eastbound carriageway on the A17 at Beckingham. A second lane appears further on but this is just a right turn lane
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Big L
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Re: Why does the UK not have any D2+1 roads?

Post by Big L »

A chunk of the A24 by Box Hill is 1 Lane south 2 lanes north.

Some of the Kidderminster to Worcester section of A449 must have been butchered to be 2+1.

Also in Worcestershire, meet the A491, by Bell End.
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