[Talk-GB] OSM Road Classification - Trunk/Primary

[Tom Hughes]

Yes it is partially a result of a misunderstanding at the
very beginning but actually it worked out well.

Whether something is actually trunk is not really that
important - whether it is part of the primary route network
is really what makes an A road more or less important than
another one.

There has long been consensus on the tagging, and there is
an equally long history of new people turning up and wanting
to change it to match the official trunk classification.

Please try and forget the words "trunk" and "primary" and
just think of them as tokens that mean more/less important.

Tom

On 14/09/2021 17:50, Barry McGuire wrote:
> It's strange that the highway=primary tag is used for non-primary 
> routes, and it seems like an historical accident caused by people 
> assuming trunk roads and primary routes are the same thing, when they're 
> not (usually). Trunk roads form part of the strategic road network and 
> are managed by a highways authority (e.g. "National Highways" formerly 
> Highways England, and their relevant counterparts in Wales and 
> Scotland). Primary routes are selected routes between primary 
> destinations. Other A roads are roads connecting important (although not 
> necessarily primary) destinations.
> 
> The Scottish OSM maps already have their strategic routes as trunk, with 
> all other A roads as primary, which more closely follows OSM terminology.
> 
> In Wales the vast majority of their primary routes are also strategic 
> (trunk) routes, but not all of them.
> 
> In England there is a proliferation of roads at the OSM 'trunk' level 
> which isn't seen in most other countries, especially not in town and 
> city centres. Many of the roads are currently tagged as 'trunk' because 
> they're primary routes but they're single carriageway, when OSM usage 
> indicates 'trunk' roads are 'high performance or high importance roads 
> that don't meet the requirement for a motorway'. This implies they 
> should be mostly dual carriageway and high importance, yet fall short of 
> motorway classification (e.g. A1, A11, A12, A14, A19, A2, A20, A23, A27, 
> A30, A31, A34, A35, A38, A4, A47, A66). This further implies that using 
> the 'strategic route' designation for the 'trunk' tag would be more 
> appropriate than using the 'primary route' designation.
> 
> Proposal to align UK road types with OSM types as follows:
> OSM Motorway = UK Motorway
> OSM Trunk = UK strategic routes, known as 'trunk' routes (Currently UK 
> primary A roads)
> OSM Primary = All other A roads (Currently UK non-primary A roads)
> OSM Secondary = B roads
> 
> Strategic route designations can be found by using data released under 
> OGLv3, just like the NaPTAN data.
> 
> There are a few edge cases to consider:-
> * B5093 Mosley Road, Fallowfield, Manchester is designated as a primary 
> route and is also a B road. Resolved by changing to strategic = trunk.
> * B6261 at Shap, Cumbria linking A6 to M6 is designated as a primary 
> route and is also a B road. Resolved by changing to strategic = trunk.
> * A505 and A602 between Stevenage and Luton are not primary routes 
> despite linking two primary destinations. The proposal would place this 
> road on the same level as all other A roads, by abolishing the 
> distinction between 'primary' and 'non-primary' A roads on OSM.
> 
> England-Scotland border (West to East) - 2 changes at the border (A7 and 
> A68)
> * M6 Motorway
> * A7 primary route (Scotland strategic, England non-strategic)
> * A68 primary route (Scotland strategic, England non-strategic)
> * A697 primary route (Scotland non-strategic, England non-strategic)
> * A1 primary route (Scotland strategic, England strategic)
> 
> England-Wales border (North to South) - 1 change at the border (A465)
> * A494 primary (Wales strategic, England strategic)
> * A55 primary (Wales strategic, England strategic)
> * A483 primary (Wales strategic, England strategic)
> * A535 primary (Wales non-strategic, England non-strategic)
> * A5 primary (Wales strategic, England strategic)
> * A483 primary (Wales strategic, England strategic)
> * A458 primary (Wales strategic, England strategic)
> * A44 primary (Wales non-strategic, England non-strategic)
> * A438 primary (Wales non-strategic, England non-strategic)
> * A465 primary (Wales strategic, England non-strategic)
> * A40 primary (Wales strategic, England strategic)
> * A48 primary (Wales non-strategic, England non-strategic)
> * M48 motorway
> * M4 motorway
> 
> Changes of designation at borders are not unusual, so I'm not concerned 
> about that.
> 
> The only real downsides to this proposal are the work involved (which 
> shouldn't really take too long) and the loss of information about which 
> roads are designed as primary - which is a bit of a false distinction in 
> any case as primary routes do not indicate the actual standard or 
> importance of the road, just that they link two 'primary locations'. 
> Note that 'primary' locations do not mean they they're actually 
> important locations, just that they're useful for navigation purposes 
> (e.g. Scotch Corner as a junction, and Stevenage for itself and the 
> towns around it). The use of those locations for navigation purposes 
> made sense in the 60s but with satnavs etc the standard and relative 
> importance of the road should take priority on maps.
> 
> Thanks,
> Barry
> 
> 
> _______________________________________________
> Talk-GB mailing list
> Talk-GB at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-gb
> 


-- 
Tom Hughes (tom at compton.nu)
http://compton.nu/