For example, the part of the A5 that parallels the M6 Toll was detrunked when the M6 Toll opened in late 2003. Yet OSM labels it as a trunk road. Why?

asked 15 Jul '10, 19:35

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NE2
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retagged 18 Jul '10, 16:18

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Jonathan Ben...
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The definition of a trunk road varies from country to country to suit local definitions. In the UK there has been a steady reduction of trunk roads as they are made the responsibly of local councils and not the Highway Agency, however the road remains an important highway in the area. The distinction used in OSM in the UK is the type of sign board: an A road with a green sign board with yellow lettering is what is used to show a highway=trunk. The black and white signs for A roads are highway=primary. This is a pragmatic approach to maintain a reasonable distinction and ignoring the political de-trunking process.

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answered 15 Jul '10, 20:18

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edited 17 Jul '10, 13:48

Good answer, but it raises a few more questions, such as why we call these "trunk" and not "primary" (since they are the "primary route network"). I guess I'm looking for a more general answer about how tags do not always mean what they seem like they should (the map is not the territory, etc.) and maybe how we have consensus to apply these definitions and revert people who use highway=trunk for, well, only trunk roads.

(15 Jul '10, 20:27) NE2
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Basically it is the way it is due to historical accident - when people started using trunk and primary they didn't realise that most of what they though were trunk roads weren't really trunk roads anymore.

So a consensus developed to instead use the two values to distinguish the primary route network from other A roads, much as the OS use two different colours on their map to distinguish the two types of A road.

(16 Jul '10, 13:38) TomH ♦♦
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question asked: 15 Jul '10, 19:35

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last updated: 18 Jul '10, 16:18

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