[Talk-GB] highway=trunk Roads and Cycle Navigation

[ianmspencer at gmail.com]

The trunk road tag on highway works differently in the UK from the usage in the rest of the world and it seriously affects interpreting routing.




Essentially, in the UK it is understood that a highway=trunk will be interpreted with the default of bicycle=yes and pedestrian=yes.




In the rest of the world, a trunk road is interpreted as being nearly a motorway and the presumption is that bicycle=no and pedestrian=no is the appropriate default.


This is a well known issue and was noted on the trunk talk page back in 2008.




This causes issues for users like myself who would like to use the prebuilt maps that other suppliers kindly produce especially as personal builds of mapping output is not for the average member of the public.




The situation is that typically UK produced map sources for Garmin (like the sterling work that TalkyToaster has done over many years) will build their translators by interpreting the attributes the GB way and of course the European producers, like Velomap, will produce them with the European interpretation. Of course, fudging the mapping is part of the art of producing good routing and various producers have invested a lot of time understanding the tricks that make routing work well (not something each individual user can invest the time in).




For various reasons, I would like to be able to select different producers, they do have different approaches to routing, and at the moment, I cannot use any other production than a UK site, and of course it means that European producers of mapping do not seem to be aware that their GB versions do not route sensibly (or rather when I raised this some years ago with one producer I got a rather Germanic blunt response to the effect of “not his problem, fix the mapping.”). Further, though I haven’t yet done him the courtesy of reporting it, there is a fault in the TT mapping where it is breaking ways so the TT mapping does not route properly at the moment.




A simple example:



Using UK Ordnance Survey coordinates, from SK 06112 33216 (Bramshall) to SK 06603 30610 (Loxley Green) is a simple route which goes along what is marked as a trunk road, Stafford Road, A518, which is way http://www.openstreetmap.org/way/222783153




In the UK, defaulting trunk roads to bicycle=no when undefined makes the mapping unusable as trivial road crossings do not route correctly and Garmin will try and route in a 10 mile diversion on a European derived Garmin map (e.g. the http://www.freizeitkarte-osm.de/ productions or http://www.velomap.org/). A cyclist would not bat an eye cycling across a typical UK road like that.


In Garmin Basecamp, flipping between different mapping products will obviously produce slightly different variations as the different producers work around routing issues by omitting or prioritising ways in different levels. However, the European derived versions will never route correctly.


Any road up, it seems to me that for some time OSM has been living with this difference and it is an unnecessary nuisance - although in context there is nothing wrong with doing it either way, it seems wrong that in crossing a border you need to implicitly be aware of a change in handling.


In my simple way of viewing things, it seems that there are two solutions - deriving a new attribute of the highway tag of trunk_uk or some suitable variant trunk_ha (highways agency) as it is essentially an administrative distinction, or explicitly setting the bicycle and pedestrian attributes to yes (except where they have already been set) so there is no real need to be aware of the distinction.


While there are workarounds that individuals can apply, it would make the OSM source far better for the Garmin user community if this small foible was resolved.


Thoughts?


Spenny
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