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nowster wrote:
The A1/A1(M) appears to have several datum points.
Three, IIRC.
At least four, London, Huntingdon and either end of Yorkshire.
Which may make this touch and go;
The information shown on a driver location sign must always be unique compared to other driver location signs, to minimise confusion following the reporting of an incident or defect. This means that a national distance referencing system should be used on driver location signs and distance marker posts along a route, i.e. the distance shown must be unique for the route, if the concept of driver location signs is to be a success. It is recommended that adjacent area teams and DBFO teams along a route should liaise to ensure that there is no duplication of distance information on distance marker posts and driver location signs along a route.
For the avoidance of doubt, this means that there must never be the same legend shown on driver location signs at different locations.
As previously noted on SABRE, the DLSs on the Tyne Tees section of A1(M) have a unique notation, involving if I remember correctly an extra letter D (perhaps standing for Durham), specially so that they can be unique while still being based on the same numbering system used on the local marker posts.
Also a long stretch of A1(M) in Yorkshire has marker posts but no DLSs, perhaps because of the uniqueness issue.
The A34's marker posts double-up at Newbury where the bypass was built. Presumably this means, if DLS were provided, special notation would be required.
Johnathan404 wrote:The A34's marker posts double-up at Newbury where the bypass was built. Presumably this means, if DLS were provided, special notation would be required.
They would probably use different carriageway identifiers - the original road being the A and B carriageways and the new road the E and F carriageways.
ais523 wrote:Travelling along the M69 recently, I was looking at the Driver Location Signs. The numbers go upwards as you go north, and downwards as you go south, which is not unreasonable. The confusing bit is that rather than reaching 0 at the south end of the motorway (which might be expected), the point at which the M69 crosses the M6 is approximately 100.
This indicates a datum point somewhere around 100 kilometres south or south-west of the M6 near Coventry, but I can't think of anything obvious. London is too distant. One possibility I considered was Strensham (because one plan for the Strensham–Solihull motorway connected to Conventry rather than Solihull and joined onto the M69), but it's too close (you can do it in under 100 kilometres along the existing motorways, and presumably a new route would be more direct). Perhaps the decision was "so we might want to extend the M69 into Coventry some time, let's just number this end 100 for future expansion".
Can anyone shed light on why this motorway has its locations numbered as they are? Any other examples of motorways with bizarre datum points?
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This is what is called a "False origin". the 100 km marker is the real origin, but scope has been left for the road to be extended in the opposite direction for an indeterminate distance (but less than 100 km). A similar thing happens with OS grid references. the UK grid is based on the 2 degree West latitude which is assigned the value of 500 km, allowing the full East-West span of the OS grid to cover 1000 kilometres. This is explained in detail in the Wikipedia article on the OS Grid.
For the record, the Bere Regis by-pass section of the A35 also starts at 100 km, obviously to allow a dual carriageway between Bournemouth and the Bere Regis by-pass without committing themselves as to where the A35 would actually start in Bournemouth.
wrinkly wrote:As previously noted on SABRE, the DLSs on the Tyne Tees section of A1(M) have a unique notation, involving if I remember correctly an extra letter D (perhaps standing for Durham), specially so that they can be unique while still being based on the same numbering system used on the local marker posts.
Also a long stretch of A1(M) in Yorkshire has marker posts but no DLSs, perhaps because of the uniqueness issue.
If you look at the DLS north of Scotch Corner, they are (or they were) all patched. Underneath, I believe, is km from London.
nowster wrote: The M56's datum point is the centre of Manchester. etc. etc.
Next time I go along I should check if there are DLS numbers along the Sharston spur or whether the 'route' ignores that part.
There are, and they're numbered the same as the rest of the M56. I guess the distance is counted along the A34
I don't understand why the A34 has to come into it. You can just continue the distances backwards along the Sharston spur from the main part of the M56, regardless of where the origin is, provided only that it's sufficiently far away that they don't reach zero before the M56 merges with the M60.
Or is the numbering on the M56 designed so that the numbers on the Sharston spur have the same origin as those on the M60 (M60 J1 = 0)?
Vierwielen wrote:..For the record, the Bere Regis by-pass section of the A35 also starts at 100 km, obviously to allow a dual carriageway between Bournemouth and the Bere Regis by-pass without committing themselves as to where the A35 would actually start in Bournemouth.
For the record, that is utter rubbish.
I agreed personally the starting chainage with the Client as we needed something to put on the marker posts and it was just a convenient number at the time with no thought of any future proofing.
wrinkly wrote:As previously noted on SABRE, the DLSs on the Tyne Tees section of A1(M) have a unique notation, involving if I remember correctly an extra letter D (perhaps standing for Durham), specially so that they can be unique while still being based on the same numbering system used on the local marker posts.
Also a long stretch of A1(M) in Yorkshire has marker posts but no DLSs, perhaps because of the uniqueness issue.
If you look at the DLS north of Scotch Corner, they are (or they were) all patched. Underneath, I believe, is km from London.
IIRC A1 in Yorkshire used London, even though the A1 south of Yorkshire used Huntingdon, as the datum point while the A1(M) in Yorkshire used Blyth.
“The simple step of a courageous individual is not to take part in the lie" - Aleksandr I. Solzhenitsyn
Johnny Mo
JohnnyMo wrote:IIRC A1 in Yorkshire used London, even though the A1 south of Yorkshire used Huntingdon, as the datum point while the A1(M) in Yorkshire used Blyth.
The AP A1 between Redhouse and Darrington (marker posts, no DLSs) uses Huntingdon. I'm not sure whether that's supposed to be relative to London minus 100, or to the start of the Alconbury-Peterborough A1(M). Probably the former, as I guess the posts antedate Alconbury-Peterborough.
I've posted previously about a small numerical difference between the Blyth-based numbers on A1(M) sections in Yorks, and the (presumably also Blyth-based) numbers on the AP A1 between Leeming Bar and Barton (soon to be replaced by new motorway ones).
Edited for spelling.
Last edited by wrinkly on Sun Oct 04, 2015 23:18, edited 1 time in total.
Vierwielen wrote:..For the record, the Bere Regis by-pass section of the A35 also starts at 100 km, obviously to allow a dual carriageway between Bournemouth and the Bere Regis by-pass without committing themselves as to where the A35 would actually start in Bournemouth.
For the record, that is utter rubbish.
I agreed personally the starting chainage with the Client as we needed something to put on the marker posts and it was just a convenient number at the time with no thought of any future proofing.
wrinkly wrote:As previously noted on SABRE, the DLSs on the Tyne Tees section of A1(M) have a unique notation, involving if I remember correctly an extra letter D (perhaps standing for Durham), specially so that they can be unique while still being based on the same numbering system used on the local marker posts.
Also a long stretch of A1(M) in Yorkshire has marker posts but no DLSs, perhaps because of the uniqueness issue.
IIRC the DLS were installed on the A1(M) using I think a Blyth datum, I seem to remember Chester-le-Street was 140 or so (I could be making that up). But then someone realised that the DLS didn't match the marker posts, so they were all plated over with different numbers. Not that I even notice them these days.
Vierwielen wrote:..For the record, the Bere Regis by-pass section of the A35 also starts at 100 km, obviously to allow a dual carriageway between Bournemouth and the Bere Regis by-pass without committing themselves as to where the A35 would actually start in Bournemouth.
For the record, that is utter rubbish.
I agreed personally the starting chainage with the Client as we needed something to put on the marker posts and it was just a convenient number at the time with no thought of any future proofing.
In which case, why did you not use zero?
IIRC this was to avoid duplication with the marker posts on the A31 Cadnam to Ringwood stretch.
wrinkly wrote:As previously noted on SABRE, the DLSs on the Tyne Tees section of A1(M) have a unique notation, involving if I remember correctly an extra letter D (perhaps standing for Durham), specially so that they can be unique while still being based on the same numbering system used on the local marker posts.
Also a long stretch of A1(M) in Yorkshire has marker posts but no DLSs, perhaps because of the uniqueness issue.
IIRC the DLS were installed on the A1(M) using I think a Blyth datum, I seem to remember Chester-le-Street was 140 or so (I could be making that up). But then someone realised that the DLS didn't match the marker posts, so they were all plated over with different numbers. Not that I even notice them these days.
The plating of the DLSs was reported on here at the time by somebody (maybe you!) so if the thread could be found it would probably tell us what the DLSs originally said.
wrinkly wrote:
The plating of the DLSs was reported on here at the time by somebody (maybe you!) so if the thread could be found it would probably tell us what the DLSs originally said.
Yes I remember and it wasn't me who noticed it first, although no doubt I commented upon it.