[Tagging] no_u_turn restrictions for every entry/exit into a roundabout when the way is split because of physical separation?

Paul Johnson baloo at ursamundi.org
Fri Apr 6 00:12:24 UTC 2018


On Thu, Apr 5, 2018 at 5:06 PM, <osm.tagging at thorsten.engler.id.au> wrote:

> I tought it was obvious, but let me spell it out: such restrictions
> represent a default which we should be recorded somewhere (not necessary
> inside OSM) once and observed by data consumers, not by creating
> potentially 100000’s of relations to again and again encode the default
> behaviour.
>

Why not have a schema, in the data, for encoding this?  Maybe a relation
with the outermost administrative area to which it applies...


> This is exactly the problem that exists in Brazil, where u-turns back onto
> the same way at intersections are generally prohibited without any explicit
> sign allowing them, so some mappers add 4 no_u_turn at every single
> intersection node.
>
>
>
> Please refer to: https://github.com/openstreetmap/iD/issues/2527
>
>
>
> In fact, it is also reapet, IN BOLD, on the main relation:restriction
> page: https://wiki.openstreetmap.org/wiki/Relation:restriction
>
>
>
> ·         *Don't map *turn restrictions that are *the default* for a
> given jurisdiction *and* are *not signed*. It is much better to ensure
> that routing engines embody the regional rule rather than mapping every
> occurrence as a turn restriction. This applies particularly to unsigned
> U-turns in Brazil, where using turn restrictions will require hundreds or
> thousands of restrictions and micro-segmentation of all roads which in turn
> make editing data hard.
>

Again, this falls back on the whole "quoting the wiki as gospel" part that
I initially beefed about.
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