Motorway DLS starting above 0 (i.e. unusual datum points)

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Arcuarius
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Re: Motorway DLS starting above 0 (i.e. unusual datum points

Post by Arcuarius »

Interesting stuff, this. I will have to have a root around in HAPMS the next chance I get.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by ais523 »

From another thread, but definitely relevant to this one:
wrinkly wrote:Seen near Tollbar End:

https://www.google.co.uk/maps/@52.37468 ... 312!8i6656

https://www.google.co.uk/maps/@52.37167 ... 312!8i6656

Where are ther A45's distances measured from?
Our best current guess is Felixstowe, which is almost exactly the right distance and does seem to make some sort of sense.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by wrinkly »

DLSs on the A38 reach 471.5 near M1 J28!

https://www.google.co.uk/maps/@53.09745 ... 312!8i6656

Numbered from Bodmin perhaps?
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by RichardA35 »

wrinkly wrote:DLSs on the A38 reach 471.5 near M1 J28!
https://www.google.co.uk/maps/@53.09745 ... 312!8i6656
Numbered from Bodmin perhaps?
Having had a few weeks working around Bodmin, the datum point of the A38 of 0/0 is at the old A30/A38 junction pre-Bodmin bypass here (Cooksland Road/Launceston Road) working back from the 2/2 post here where the A38 crosses the Bodmin bypass.
A quick routeplan going through as many city centres as possible gives the distance as ~470km.....
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Jeni »

RichardA35 wrote:Having had a few weeks working around Bodmin, the datum point of the A38 of 0/0 is at the old A30/A38 junction pre-Bodmin bypass here (Cooksland Road/Launceston Road) working back from the 2/2 post here where the A38 crosses the Bodmin bypass.
A quick routeplan going through as many city centres as possible gives the distance as ~470km.....
Please correct me if I'm wrong, but I don't think the A38 ever terminated at that point.

https://www.sabre-roads.org.uk/maps/ind ... 14&layer=1
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by RichardA35 »

Jeni wrote:
RichardA35 wrote:Having had a few weeks working around Bodmin, the datum point of the A38 of 0/0 is at the old A30/A38 junction pre-Bodmin bypass here (Cooksland Road/Launceston Road) working back from the 2/2 post here where the A38 crosses the Bodmin bypass.
A quick routeplan going through as many city centres as possible gives the distance as ~470km.....
Please correct me if I'm wrong, but I don't think the A38 ever terminated at that point.

https://www.sabre-roads.org.uk/maps/ind ... 14&layer=1
Yes I think you are right, so I must be talking about a "post Bodmin Bypass" start of the A38 which is probably more contemporary with the time when marker posts started to be used.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Chris5156 »

Time to bump this age-old topic.

I've just been looking at the M6 Toll's markerpost numbering and it turns out to be another motorway with a seemingly arbitrary zero point. I'd expected it to share the M6's numbers, which in turn follow those from the M1. But it doesn't, and nor does it follow the M42's numbering scheme, even though the two share carriageway for a short distance.

Instead it begins, at M6 J3A, at around 9.5km. For comparison, the parallel markerposts on the M6 itself show 168.5km here. If you measure 9.5km eastwards, it appears the nominal origin point for the M6 Toll is where the east-facing sliproads from Corley Services meet the M6, or somewhere thereabouts. What's that all about?
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Re: Motorway DLS starting above 0 (i.e. unusual datum points

Post by solocle »

Lockwood wrote: Mon Sep 28, 2015 08:09 Other example: The M271 uses the M27's , so as you head off the M27 towards Southampton you are met with 11.0, and the DLS from the M271 E/B towards Rownhams are in the 11.x range
For some real fun the lowest sign you'll find on the M27 is 1.7, at the Cadnam Interchange. It seems the datum point is around the next junction along the A31, for Minstead.

Meanwhile the A31's datum point is at the Cadnam interchange, counting up as you head West.
Image
Image

From the SABRE Wiki: Cadnam Interchange :

Cadnam Interchange is junction 1 of the M27.

It is the only motorway junction inside a national park, though until the national park was created, the New Forest boundary skirted the junction. Despite being the western terminus of the M27, the junction has three lanes through it, but the A31 to the west is only two lanes. This creates a bottleneck where the 3-lane M27 and 2-lane on-slip merge into the 2-lane A31 in a short distance.

Most maps published in the

... Read More
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Re: Motorway DLS starting above 0 (i.e. unusual datum points

Post by Vierwielen »

solocle wrote: Thu Jul 28, 2022 15:48
Lockwood wrote: Mon Sep 28, 2015 08:09 Other example: The M271 uses the M27's , so as you head off the M27 towards Southampton you are met with 11.0, and the DLS from the M271 E/B towards Rownhams are in the 11.x range
For some real fun the lowest sign you'll find on the M27 is 1.7, at the Cadnam Interchange. It seems the datum point is around the next junction along the A31, for Minstead.

Meanwhile the A31's datum point is at the Cadnam interchange, counting up as you head West.

... images deleted...
Wikimedia Commons has an image of the M27 2.7 km driver location sign which is about one kilometre from the start of the aforementioned A31 zero point.

From the SABRE Wiki: Cadnam Interchange :

Cadnam Interchange is junction 1 of the M27.

It is the only motorway junction inside a national park, though until the national park was created, the New Forest boundary skirted the junction. Despite being the western terminus of the M27, the junction has three lanes through it, but the A31 to the west is only two lanes. This creates a bottleneck where the 3-lane M27 and 2-lane on-slip merge into the 2-lane A31 in a short distance.

Most maps published in the

... Read More
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Re: Motorway DLS starting above 0 (i.e. unusual datum points

Post by solocle »

Vierwielen wrote: Thu Jul 28, 2022 17:55
solocle wrote: Thu Jul 28, 2022 15:48
Lockwood wrote: Mon Sep 28, 2015 08:09 Other example: The M271 uses the M27's , so as you head off the M27 towards Southampton you are met with 11.0, and the DLS from the M271 E/B towards Rownhams are in the 11.x range
For some real fun the lowest sign you'll find on the M27 is 1.7, at the Cadnam Interchange. It seems the datum point is around the next junction along the A31, for Minstead.

Meanwhile the A31's datum point is at the Cadnam interchange, counting up as you head West.

... images deleted...
Wikimedia Commons has an image of the M27 2.7 km driver location sign which is about one kilometre from the start of the aforementioned A31 zero point.
There's a DLS just before the end of the M27 - https://www.google.co.uk/maps/@50.91967 ... 8192?hl=en

There isn't an intermediate marker post, so the motorway certainly ends before the 1.6 km mark, although interestingly it's very close to one mile...

From the SABRE Wiki: Cadnam Interchange :

Cadnam Interchange is junction 1 of the M27.

It is the only motorway junction inside a national park, though until the national park was created, the New Forest boundary skirted the junction. Despite being the western terminus of the M27, the junction has three lanes through it, but the A31 to the west is only two lanes. This creates a bottleneck where the 3-lane M27 and 2-lane on-slip merge into the 2-lane A31 in a short distance.

Most maps published in the

... Read More
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by jervi »

Since this thread has risen I'd mention some weird datum and carriageway references on the M23/A23.

The Trunk A23 has its datum point at the Mill Road Roundabout (A27) and counts up as it goes North.
This is the most Northern marker just before it meets the M23 - https://www.google.co.uk/maps/@51.08438 ... 384!8i8192 - 25.8
The M23 has its datum point somewhere in central London and counts up as it goes South.
This is the most Southern marker just before it meets the A23 - https://www.google.co.uk/maps/@51.08507 ... 384!8i8192 - 53.8

The strange thing is that the bridges along the A23 use the M23's datum.
https://www.google.co.uk/maps/@51.08331 ... 384!8i8192 - The first one somewhat makes sense, its about 150 meters from the end/start of the M23 and was constructed as part of the original M23 build.
https://www.google.co.uk/maps/@51.07490 ... 384!8i8192 - The second bridge however makes less sense. It was built in about 94 and nearly 1km away from the M23.
https://www.google.co.uk/maps/@51.03831 ... 384!8i8192 - Here two bridges carry each carriageway, A & B are used as if counting up heading South (like the M23)
https://www.google.co.uk/maps/@50.87116 ... 384!8i8192 - The last bridge before the A27 using the M23 datum point.
This continues to every single bridge along the A23 to the A27. There two exceptions.
One is the Subway between Handcross & Warninglid junction which was built in 2012-14 & the other being the bridge that carries the A27 over the A23.

Another weird thing is that A&B carriageways seem to be the wrong way around.
As far as I am aware the carriageway where distance counts up is always the "A" carriageway, and the other is the "B" carriageway. This means that the A & B carriageways switch at Junction 11, and South of J11 as you head towards Brighton you are on the B carriageway as the distance counts down. However the Variable Message Signs have the A carriageway designation rather than B. https://www.google.co.uk/maps/@50.89561 ... 384!8i8192
https://www.google.co.uk/maps/@50.86850 ... 384!8i8192 - Roadside cabinets reinforces that the B carriageway is counting up, not down.


If the A23 just used the M23's datum everything would make sense. Buts its just strange that A23 uses the A27 as its datum, which was probably defined in the early 90s, despite bridges already using the M23's datum, and then to get the A & B carriageways the wrong way around as well.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Chris5156 »

jervi wrote: Fri Jul 29, 2022 10:37If the A23 just used the M23's datum everything would make sense. Buts its just strange that A23 uses the A27 as its datum, which was probably defined in the early 90s, despite bridges already using the M23's datum, and then to get the A & B carriageways the wrong way around as well.
I think I mentioned upthread that one of the remarkable things about this weird setup is that, because the M23 starts so far from central London and its lowest marker post is so far above zero, there are no duplicated numbers on the A23/M23 route even though it uses two totally unrelated systems. Surely just a fluke, but a very lucky one.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by wrinkly »

Chris5156 wrote: Fri Jul 29, 2022 12:06 I think I mentioned upthread that one of the remarkable things about this weird setup is that, because the M23 starts so far from central London and its lowest marker post is so far above zero, there are no duplicated numbers on the A23/M23 route even though it uses two totally unrelated systems. Surely just a fluke, but a very lucky one.
Likewise marker post numbers on the M6, A74(M) and M74 are unique on the entire route, though the numbering system changes from London-based to Glasgow-based at at Johnstonebridge.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Vierwielen »

Chris5156 wrote: Fri Jul 29, 2022 12:06
jervi wrote: Fri Jul 29, 2022 10:37If the A23 just used the M23's datum everything would make sense. Buts its just strange that A23 uses the A27 as its datum, which was probably defined in the early 90s, despite bridges already using the M23's datum, and then to get the A & B carriageways the wrong way around as well.
I think I mentioned upthread that one of the remarkable things about this weird setup is that, because the M23 starts so far from central London and its lowest marker post is so far above zero, there are no duplicated numbers on the A23/M23 route even though it uses two totally unrelated systems. Surely just a fluke, but a very lucky one.
The M23 was due to start onRingway 2, but Ringway 2 never happened and the South Circular remains a bottleneck.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Osthagen »

On the A1(M) between Washington and Barton, the datum number on the DLSs is patched over. The patches themselves contain the distance in KM to J56 (Barton), although I can't comment on what's underneath.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by wrinkly »

Osthagen wrote: Sun Oct 23, 2022 02:20 On the A1(M) between Washington and Barton, the datum number on the DLSs is patched over. The patches themselves contain the distance in KM to J56 (Barton), although I can't comment on what's underneath.
The patches also have an extra D on them (for Durham?) because otherwise they would be theoretically ambiguous, capable of suggesting somewhere much further south on the A1(M). Because of the non-standard D, they do not fully comply with the standard for what should be on a DLS.

https://www.google.co.uk/maps/@54.47669 ... 384!8i8192

The information on what is under the patches is in an old thread here somewhere.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Chris Bertram »

wrinkly wrote: Sun Oct 23, 2022 14:30
Osthagen wrote: Sun Oct 23, 2022 02:20 On the A1(M) between Washington and Barton, the datum number on the DLSs is patched over. The patches themselves contain the distance in KM to J56 (Barton), although I can't comment on what's underneath.
The patches also have an extra D on them (for Durham?) because otherwise they would be theoretically ambiguous, capable of suggesting somewhere much further south on the A1(M). Because of the non-standard D, they do not fully comply with the standard for what should be on a DLS.

https://www.google.co.uk/maps/@54.47669 ... 384!8i8192

The information on what is under the patches is in an old thread here somewhere.
The "Durham" section of A1(M) begins in the North Riding of Yorkshire, modern North Yorkshire, and doesn't enter Durham until it crosses the Tees about 4 miles north of Barton. A66(M) is entirely south of the Tees.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Vierwielen »

wrinkly wrote: Sun Oct 23, 2022 14:30
Osthagen wrote: Sun Oct 23, 2022 02:20 On the A1(M) between Washington and Barton, the datum number on the DLSs is patched over. The patches themselves contain the distance in KM to J56 (Barton), although I can't comment on what's underneath.
The patches also have an extra D on them (for Durham?) because otherwise they would be theoretically ambiguous, capable of suggesting somewhere much further south on the A1(M). Because of the non-standard D, they do not fully comply with the standard for what should be on a DLS.

https://www.google.co.uk/maps/@54.47669 ... 384!8i8192

The information on what is under the patches is in an old thread here somewhere.
One possibility is that since there are number sets of numbers on the A1(M), one of the sections is denoted by "D" and others possibly by "A", "B" and "C". Since this is really only of interest to the Highway Agency (or whatever they call themselves these days) and to Sabristi, nothing will be done until metrication of road signs is rolled out, when a coherent system will be put into place as a "learning aid" for drivers.
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Glen »

Osthagen wrote: Sun Oct 23, 2022 02:20 On the A1(M) between Washington and Barton, the datum number on the DLSs is patched over. The patches themselves contain the distance in KM to J56 (Barton), although I can't comment on what's underneath.
In the centre of Barton junction it switches from 139.2 to 0/5 D.
Barton.JPG
https://goo.gl/maps/GV28pjMC2yNz4QSL6
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Re: Motorway DLS starting above 0 (i.e. unusual datum points)

Post by Glen »

On the AWPR, the A90 counts up from 00.0 at Stonehaven; whereas the A956 counts up from 50.0 at Charleston, towards Cleanhill.

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