[OSM-talk] UK: Trunk-Primary

Tom Hughes tom at compton.nu
Mon Aug 13 00:35:40 BST 2007

In message <BLU115-F9CBFB90556EB78A4300BCCFE30 at phx.gbl>
          "Ben Robbins" <ben_robbins_ at hotmail.com> wrote:

> Proposal for "signage=<colour>", or somethign to similar effect, so that
> green signed primary roads, and green signed trunk roads can be split
> appart.

That is, to be completely frank, a ludicrous proposal. Tagging something
explicitly based on the colour of the signs is just ridiculous.

What is important is not whether the sign is green or white, but the
categorisation of the road - green signs indicate primary A roads and
white signs indicate secondary A roads. Hence what is important is not
the colour of the signs but the class of the road (which happens to be
implied by the colour of the signs).

So the highway tag is the right place to record this information, not
some new tag that records the colour of the road signs.

> For A roads in the UK there are 3 different main groups
> 1) Trunk Roads, roads managed by HA of A road status, rather than motorway
> 2) Primary Roads, roads which aren’t HA (according to the governments list
> on wiki), but have green signs.
> 3) Primary Roads, roads which aren’t HA, and don't have green signs.
> In OSM most people take trunk to mean a primary road with green signs (2),
> but I'm not really shore why.

The reason is that there are very few HA managed A roads left, and they
are getting fewer all the time as the HA palms them off to the local
highway authorities. As a results the traditional trunk road concept is
now more or less meaningless.

> The problem is that a lot of primary roads that are not on the governments
> list, on the wiki, or on there website (which seems to be more updated) are
> being merged under the same tag as ones that are.  Yet they are very
> different.  Primary with and without green signs are very similar, while
> trunk and primary+green, are noticeably different.  So we have 2 tags that
> are being used for similar roads, and 1 tag for 2 different roads.

That's just nonsense though. Your example of trunk on IRC was a dual
carriageway section of the A43 which looked very similar to the A10 near
me (used to be HA maintained trunk, but is no longer) and the A414 near
me (has never been HA maintained trunk).

Large chunks of the A10 in Herfordshire are even grade separated, as are
some junctions on the A414.

> Really the difference between primary and trunk is either signage, or
> management,  depending which we go on; and not the highway type at all.  But
> there isn't any real problem with it being under highway, and it's more
> suitable for people in other countries I would think.  The question is what
> matters?   What matters in my opinion is being able to use the maps to plan
> a journey, and dividing the A roads by management does this indirectly, as
> HA roads are a lot faster nearly always (don't list exceptions please),
> while the signage doesn’t state anything, and in fact the merging of real
> trunk and green signed roads would mean fast and slow roads are mixed so if
> anything it devalues a tag, as you can't predict the average speed unless
> its stated separately.

I'm sorry, but exceptions are important. Actually it's not even
exceptions these days - the vast majority of fast (ie roughly
motorway equivalent speed) grade separated dual carriageway A roads
are not HA maintained now.

That essentially makes your argument (that HA maintained trunk
roads are somehow important to route planners because they are
better than ordinary primary A roads) completely moot.


Tom Hughes (tom at compton.nu)

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