[OSM-talk] UK: Trunk-Primary

Ben Robbins ben_robbins_ at hotmail.com
Mon Aug 13 00:13:19 BST 2007

This question is UK based, but I think the solution could be made helpful to 
all.  I'll right this email in short then long, cuase its a simple point, 
but I'll try and cover everything.


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


For A roads in the UK there are 3 different main groups…(sorta)

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 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.

If you added all tags like lanes= it still doesn't really round up what it 
is. Nobody would be able to filter out real trunk roads from the database as 
using this method they would be physically described as being different from 
the trunk, rather than have 1 searchable tag.

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.

Personally I think it would make more sense to tag the roads that are part 
of the HA as trunk or motorway, and add signage=green for other roads. (or a 
tag to the same effect)

This would mean that people who want can find the UK's trunk roads from 
OSM's data, and people can also find all green signed roads.  It also means 
anyone else could use this tag anywhere where they think the signage is 
important.  It also means a rendering program can chose weather to render 
based on signage or management, rather than OSM making that decision for 

In my opinion it wouldn't matter so much if something is tagged badly as 
long as it’s tagged with enough individualism that it can be identified and 
converted to the standardised way later on, but if many different things are 
tagged as being the same, then there’s a problem, as its impossible to 
filter x's out of a pile of x's.

A few examples of green signed primary roads are (all or elements of the): 
A140, A148, A15, A44, A429, A41, A422 etc.etc.  They have green signs (as 
far as I remeber), but do not appear on the highway.gov list of trunk roads. 
   If I wanted to mimic their map, I couldn’t without copying.

note: signage= may be able to be used for some other things.


p.s. There is an updated map on the .gov site that the wiki links to on the 
trunk page, is it legal to copy from this to check what is/isn't trunk? or 
was the data on the wiki taken from a database or something none graphicy?



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