[Tagging] Permissive turn restrictions

[Paul Johnson]

On Thu, Sep 1, 2016 at 7:10 AM, Martin Koppenhoefer <dieterdreist at gmail.com>
wrote:
>
>
> > Il giorno 01 set 2016, alle ore 12:00, Nick Hocking <
> nick.hocking at gmail.com> ha scritto:
> >
> > Turn restriction seem to be either mandatory (only) or prohibitive (no)
> but I think we need a permissive one, maybe (allowed)
>
>
> Why not (also) map the ones where it isn't allowed? You probably can't
> count on routing software implementing all country specific defaults (at
> least currently it isn't the case with the popular osm-based ones, so they
> need specific advice from the mappers in order to work well).
>

Let's see, for one area in the US let's start off with creating 3+
no-u-turn relations for every intersection that has a yield sign, stop sign
or traffic signal in all of Oregon and (very likely, since they're usually
on par with Oregon) Idaho and Washington State, minus maybe a few hundred
where signs explicitly allow u-turns.  I would honestly be surprised if
that doesn't put us at least well into 7 figures of new relations just
right there.  I've brought this up in previous threads personally regarding
that region.


> From a practical point of view, routing engines will generally be very
> reluctant to suggest u-turns, because they tend to take a lot of time or
> might even be close to impossible (with lots of traffic).
>

Ideally, this should be a user-selectable option (to select the user's
preference/locale's default), overridden by the appropriate relation
(no-u-turn or (and I'm proposing this) u-turn-ok) for smaller vehicles
(bicycle, car, motorcycle...), and literally short of hell or high water
avoid for more difficult to turn modes (bus, goods, hgv, horsebuggy...).
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