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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