Proposal:Change the meaning of the UK highway trunk and primary tags

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Change the meaning of the UK highway trunk and primary tags
Proposal status: Proposed (under way)
Proposed by: Barry86m
Draft started: 2021-09-15
RFC start: 2021-09-16

Proposal

Propose a change to the UK OSM guidance for trunk and primary highway tags. This will allow for easier future maintainability by aligning the definitions with publicly available datasets, more closely align with global OSM terminology and also align with common UK terminology.

No new database elements. Updated UK guidance for:

Exact proposal will depend on community discussion and feedback.

Rationale

There is an impetus to change as there is a data maintainability issue with primary routes due to no central authority and no public dataset of primary routes. Primary routes are meant to have signs with green backgrounds, but this is not necessarily always the case so there can be conflicts between surveys and information obtained from local authorities. There are datasets released under Open Government Licence (OGL) available for other types of designation (e.g. Strategic Routes and Major Roads) which may be suitable for direct use. Scottish contributors have already changed their definition to Transport Scotland's Strategic/Trunk routes due to perceived de-primarying of certain routes as indicated by new signs having a white background, which means the remaining roads fall solely within the Strategic/Trunk designation. Changing to using public datasets means the definition is verifiable, although not necessarily on the ground.

There is also a proliferation of OSM 'trunk' roads in the UK, particularly in England, to a level that is not often seen in other countries especially not in developed European nations. Some of those roads are relatively minor in nature and do not, on the face of it, appear to warrant a status of 'trunk' in importance.

There is also a resistance to change due to the long-standing community definition that primary = trunk. There are regular queries about why OSM uses primary routes as trunk, when trunk routes are defined by government as strategic routes. It appears the reason is OSM UK started with that definition and that is what has stuck. Primary routes are mostly, although not always, verifiable on the ground via signage colour. Some contributors have acknowledged the current system is not perfect and likely not something one would choose if starting again.

OSM Global Definitions

OSM globally defines the usage of the trunk tag for:

  • The most important roads in a country's system that aren't motorways. (Need not necessarily be a divided highway.)
  • High performance or high importance roads that don't meet the requirement for motorway.

It defines the primary tag for:

  • The next most important roads in a country's system. (Often link larger towns.)
  • A major highway linking large towns.

Actual usage of these terms lies on a continuum as they do not necessarily align directly to a country's own classification systems, so the community needs to decide how to apply the general definitions to their own situation. The current UK OSM definition for 'trunk' is towards one end of this continuum, but is not an outlier.

Roads tagged as motorways or trunk are rendered at zoom level 6, with roads tagged primary rendered at zoom level 8. This adds weight to the trunk tag's usage as 'nearly motorway' in importance.

Current UK OSM definitions

OSM UK definition
Motorway Roads under Motorway Regulation.
Trunk A-roads with primary status (signed yellow on green)
Primary A-roads with non-primary status (signed black on white)
Secondary B-roads

UK Roads Hierarchy

The very brief hierarchy is presented here for reference. Note that it is not always appropriate to take a government's classification and transpose it directly into OSM (e.g. Many of Kenya's "International Trunk Roads" are generally classified as primary rather than trunk due to their features and relatively low importance). It is helpful to have an external authority to provide specific categories and designations in a manner that is easy for OSM contributors to use, which can prevent arguments about borderline cases. It is then up to the OSM community to decide which external category applies to which OSM tag. The primary route designation is not easy to use, as described below.

Road Type Comment
Motorway Has a motorway designation and are nearly always managed by a national highways authority. Management exceptions are mostly confined to city centre motorways (e.g. Leeds, Newcastle)
Strategic routes Those routes managed by or on behalf of a Highways Authority (e.g. National Highways, formerly Highways England formerly Highways Agency - and the relevant counterparts in Wales and Scotland). This classification started out as trunk roads in 1936, expanded significantly, then when it was handed over to Highways Authorities many roads were de-trunked to allow those authorities (particularly the Highways Agency) to focus on the core routes. The non-trunk routes were retained by/handed back to local authorities.

Strategic route data is published by the relevant agency under OGLv3, so may be suitable for direct usage:

Primary routes (usually A-roads) / Major roads Primary routes were introduced in the 1960s to aid navigation during the large increase in car ownership. They connect approximately 350 primary destinations designated by government. The routes themselves are decided by Local Authorities and are meant to be signposted with green backgrounds. There is no central dataset of primary routes. Instead the data must be obtained from local authorities or from surveys. The problem with obtaining data from LAs is that it can take an excessive amount of work. The problem with surveys is that the primary route may change and the signage may not be adequately updated, or may be replaced in an incorrect colour by contractors (it has been known!). Some primary routes (e.g. A272 West of the A24) have white signage instead of green. Street photography may be unavailable or out of date so requires travel to a location to double check signs that may not be totally accurate in any case. There is not an easy way to keep track of primary route designations.

In Wales, primary routes are nearly always also Strategic/Trunk routes, but there are exceptions. In Scotland, it is believed Strategic/Trunk and primary routes are the same, although green signs remain on presumed former primary routes - replacement signs on those routes are usually white (e.g. A697).

Major Roads

In the late 2010s the Department for Transport introduced a 'Major Roads' category in England that is quite closely aligned to the primary routes. They define major roads as daily traffic flows of 20,000 or greater, or over 10,000 with a high proportion of HGV/LGV use. They also include some 'near miss' routes that are deemed important e.g. diversionary routes, linking population centres of greater than 25,000 residents. It is unclear whether this designation is temporary for road funding purposes or intended to be permanent, and if so whether there is any intention to merge it with the primary route definition. There is a dataset available for download under OGLv3, so may be suitable for direct usage:

Some roads appear to have been included as a means to gain funding needed now, rather than long-term importance.

Class B primary routes

There are (at least) two very short class B primary routes created contrary to the government's primary route guidance; B6261 at Shap, Cumbria linking A6 to M6, and the B5093 Mosley Road, Fallowfield, Manchester. Neither of those are in the Major roads dataset.

Other A roads Intended to provide large-scale transport links within or between areas. May have between 1 and 4 numbers. Single number roads are considered historically more important, with more digits used for roads that are newer or less important. Many of the older single (or double) digit A roads have been upgraded to a higher standard so may have increased in importance, or have new motorways running near them so their importance may be downgraded due to most traffic now using the motorway. A 4 digit A road may still be important, but usually on a regional scale rather than nationally. Using the number of digits to determine importance is a very rough approximation and cannot be relied upon.
B roads Intended to connect different areas, and to feed traffic between A roads and smaller roads on the network.
Local minor classifications (e.g. C, D, U) There is no national standard for local minor classifications and those road numbers may be repeated across local authority boundaries. They are used by local authorities as an internal mechanism to keep track of their classified roads - many of their classified roads may not be given a local route number and instead referred to by name. Local minor route numbers should not be displayed on signage.
Unclassified roads, tracks, private roads etc Local roads intended for local traffic e.g. within housing estates, some village centres, farm tracks, private estates where there is an implied right of access.

Examples

This is a sample of roads in England to help determine which UK type is most appropriate to be aligned with the OSM trunk road type. In Wales and Scotland the strategic and primary routes are more closely aligned so it does not make much sense to analyse the differences here.

The OSM global definitions column is a judgement based on road features and national importance, using the global definitions as a guide to determine an approximately average categorisation. This is not an exact science as the categorisation falls within a range. Number of lanes are each way.

Road Link Physical features OSM global (approximation) Current OSM UK Strategic Major Road Primary Route
A11 (nr Thetford) https://www.mapillary.com/app/?pKey=1567401983606112 two lane dual carriageway, roundabouts trunk (maybe primary) trunk Y Y Y
A19 (North of Thirsk) https://www.mapillary.com/app/?pKey=896183941222127 two lane dual carriageway, some grade separated junctions trunk trunk Y Y Y
A19 (South of York) https://www.mapillary.com/app/?pKey=206590181079154 one lane single carriageway primary (maybe trunk) trunk N Y Y
A30 (Near Bodmin) https://www.mapillary.com/app/?pKey=393642712031574 two lane dual carriageway, grade separated junctions trunk trunk Y Y Y
A34 (Near M4) https://www.mapillary.com/app/?pKey=976699476421225 two lane dual carriageway, grade separated junctions trunk trunk Y Y Y
A34 (Newcastle-under-Lyme) https://www.mapillary.com/app/?pKey=474757013824438 40mph limit, two lane dual carriageway, traffic lights, roundabouts, preference for through traffic to use A500 primary (maybe trunk) trunk N Y Y
A39/A390 (Near Truro) https://www.mapillary.com/app/?pKey=3152102695023717 two lane dual carriageway, roundabouts, traffic lights, no central barrier primary (maybe trunk) trunk N Y Y
A406 (London North Circular) https://www.mapillary.com/app/?pKey=778382206154070 50mph limit, two lane dual carriageway, grade separated junctions, red route trunk trunk N Y Y
A50 (Near Uttoxeter) https://www.mapillary.com/app/?pKey=224592432350948 Some 40mph limit at roundabouts, two lane dual carriageway, some roundabouts with proposal to grade separate trunk (maybe primary until upgrades complete) trunk Y Y Y
A500 (Stoke/Newcastle-under-Lyme) https://www.mapillary.com/app/?pKey=325387342548844 50mph limit, three lane dual carriageway, grade separated junctions trunk trunk Y Y Y
A64 (Leeds) https://www.mapillary.com/app/?pKey=4013475718728727 40mph limit, two lane dual carriageway, traffic lights, roundabouts, preference for traffic to use M621 primary (maybe trunk) trunk N N Y
A64 (York) https://www.mapillary.com/app/?pKey=235125565055206 two lane dual carriageway, grade separated junctions trunk trunk Y Y Y
A65 (nr Yeadon) None on Mapillary 30mph limit, one lane single carriageway, roundabouts primary primary N Y N
A658 (nr Yeadon) https://www.mapillary.com/app/?pKey=212812803761728
B-road give way: https://www.mapillary.com/app/?pKey=980797316059596		 30mph limit, one lane single carriageway, roundabouts, gives way at a junction with a B-road primary trunk N Y Y
A660 (Headingley) https://www.mapillary.com/app/?pKey=954123805127358 30mph limit, one lane single carriageway, traffic lights primary trunk N N Y
A66 (Scotch Corner to Penrith) https://www.mapillary.com/app/?pKey=1469694183372646 Mostly national speed limit, some sections with speed limits as low as 40mph (due to roadworks), mostly dual carriageway, although there are some lengthy one lane single carriageway sections trunk trunk Y Y Y

None of the classifications match up neatly with an approximate global average classification. That is the nature of applying national categorisations to a global definition, particularly where (as in the UK) we have multiple overlapping classifications (e.g. A roads can be motorways, or primary, or major, or strategic, or multiple categories, or none)

In the UK with standard of the core road infrastructure, it seems unnecessary to have 30mph one lane single carriageways designated as 'trunk'. That is not to say that 'trunk' roads should be defined by their features (e.g. dual carriageway) - that is only part of it. They should be mostly defined by their importance. When looking at the most important roads as defined by government (i.e. strategic/trunk roads), some of those are partly single carriageway and due to their relatively limited number and national importance it appears to be an appropriate use of the OSM trunk guidance's "need not necessarily be a divided highway". Small 30mph roads do not seem fitting of the criteria of "high performance or high importance roads that don't meet the requirement for motorway".

Particular cases to highlight are:

  • A658 near Yeadon which is primary and the A65 near Yeadon which is not primary - both have similar physical features and carry similar levels of traffic. Both are included in the Major Roads dataset and neither are classed as Strategic Roads. Since two of three government categorisation methods are in agreement (plus both are class A roads), they are of similar importance, yet using the primary route designation for OSM means they appear to be very different in nature. This exaggerates extremely minor differences and is very noticeable when they are in such close proximity.
  • A66 Scotch Corner to Penrith - All three categorisation methods are in agreement that this is an important road, yet parts of it are single carriageway sometimes with speed limits as low as 40mph (road works). Appropriate use of the "need not necessarily be a divided highway".
  • A406 London North Circular road is sufficiently important to be defined as 'trunk'. It does not appear on the strategic route map due to being in London, but is a primary route and appears on the major roads dataset.

Tagging/Options

Keep the status quo (OSM Trunk = primary routes, except Scotland)

  • Data quality issues - No central authority for routes. Data not publicly available. Reliance on surveys or FoI requests, which both have problems (e.g. surveys may not be accurate, FoI can take an excessive amount of work, and data from surveys and FoI requests may conflict). This increases the likelihood of contributors using non ODbL compliant sources (e.g. OS Maps).
  • Confusion for new editors and members of the public (trunk = primary, primary = non-primary).
  • In Scotland, the strategic road map is used for OSM trunk. Some of the non-strategic primaries have started to gain white signs when needing replacements which implies they have been downgraded, although a lot of green signs remain. This further highlights the maintainability issues and the need to have a good data source.
  • The public generally associates trunk routes as large roads with possible access restrictions (e.g. no cycling or horses) which is not necessarily true for strategic routes, never mind primary routes.
  • Category in continuous use since the 1960s.
  • Stays consistent with UK OS maps.
  • Primary routes aren't the most important roads (as defined by government) so are not fully consistent with global OSM guidance. The UK is not an outlier in this respect.
  • Examples of similar roads in close proximity with very similar features and relative importance levels, but having different primary route classifications.
OSM highway tag England Wales Scotland
Motorway Motorway Motorway Motorway
Trunk Primary Primary Strategic/Primary
Primary Other A roads Other A roads Other A roads
Secondary B roads B roads B roads

Change UK OSM trunk to mean Major Roads (and OSM primary to all other A roads)

  • Well defined because a dataset is centrally published and is available under OGLv3, so may be suitable for direct use.
  • Category has only been in place for approximately 4 years.
  • Uncertainty over whether this category will be long-term, or simply used for short-term road funding, or eventually merge with the primary route definition.
  • In Wales since there is little difference between strategic and primary routes, their strategic/trunk route data could be used as the definitive version.
  • In Scotland, the strategic road map is used for OSM trunk as mentioned above.
  • Major Road Links with Scotland tally with their Strategic/Trunk designation. Some roads designated as Major in England are not designated as Strategic/Trunk in Wales so there will be some changes at the border.
  • Reduced confusion for new editors and members of the public (trunk = major, primary = non-major A).
  • The public generally associates trunk routes as large roads with possible access restrictions (e.g. no cycling or horses) which is not necessarily true for strategic routes, never mind major routes.
  • Broadly consistent with UK OS maps.
  • Major roads aren't the most important roads (as defined by government) so are not fully consistent with global OSM guidance. The UK is not an outlier in this respect.
  • Includes nearly the same roads as the current primary routes which limits the number of changes needed.
OSM highway tag England Wales Scotland
Motorway Motorway Motorway Motorway
Trunk Major Strategic Strategic
Primary Other A roads Other A roads Other A roads
Secondary B roads B roads B roads

Change UK OSM trunk to mean Strategic routes (and OSM primary to all other A roads)

  • Well defined because the dataset is centrally published and is available under OGLv3, so may be suitable for direct use.
  • It will take more work to update it as many more roads will need changing from trunk to primary.
  • They are the most important non-motorways.
  • Category in continuous use in one form or another since the 1930s.
  • Better aligns with global OSM definitions and would place the application of the trunk tag more centrally in the continuum of global OSM usage.
  • This definition also reflects UK terminology (strategic = trunk), although there is a relatively common misconception that primary routes and trunk roads are the same thing.
  • Loss of current primary/non-primary distinction:
    • potential mitigation by moving non-primary A roads to OSM secondary, that would push B roads to OSM tertiary, then minor classified to unclassified. This introduces confusion and more work, so best avoided.
    • it is difficult to maintain the data needed to keep this current distinction
  • There are limited strategic routes in London because most routes that fit a strategic/trunk description are the responsibility of Transport for London and they do not designate roads as strategic or trunk. An alternative definition will need to be used within the M25. TfL's red routes are generally similar to London's primary routes, yet slightly more numerous. Major routes could be a good compromise.
  • Possible implications for downstream data uses.
OSM highway tag England Within M25 Wales Scotland
Motorway Motorway Motorway Motorway Motorway
Trunk Strategic Strategic or Major Strategic Strategic
Primary Other A roads Other A roads Other A roads Other A roads
Secondary B roads B roads B roads B roads

Features/Pages affected

Roads in the United Kingdom

Further Reading


External discussions

Comments

Please comment on the discussion page.

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