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

[Robert Whittaker (OSM lists)]

FYI: The wiki page describing (what should be) the current situation
for road tagging across the UK is at
https://wiki.openstreetmap.org/wiki/Roads_in_the_United_Kingdom . In
all UK countries, the primary route network (signified by green signs)
should be highway=trunk, and other A-roads should be highway=primary.
It's been set up this way for ages. I assume the tagging convention is
the result of (a) it being easier to verify green signs on the ground,
and (b) OS's 1:50k maps also making the distinction between primary
and non-primary A roads in their colouring. (The OSM highway colours
originally followed the OS colour scheme, with highway=trunk in green
and highway=motorway in blue.) I guess the tag names used were the
result of a misunderstanding of the highways terminology.

According to the thread at
https://www.sabre-roads.org.uk/forum/viewtopic.php?t=39829 there are
very few non-trunk primary network roads in Scotland and Wales, which
may explain your observation about the tagging there.

Personally, I think I'd be in favour of sticking to the status quo. In
terms of looking at the map for route planning, it seems more
beneficial to have all the primary network routes highlighted, rather
than just the sparser trunk road network.

Robert.

On Tue, 14 Sept 2021 at 17:53, Barry McGuire <barry86m at gmail.com> 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

-- 
Robert Whittaker
https://osm.mathmos.net/