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

Kevin Kenny kevin.b.kenny+osm at gmail.com
Fri Apr 6 04:04:31 UTC 2018

On Thu, Apr 5, 2018 at 9:50 PM,  <osm.tagging at thorsten.engler.id.au> wrote:
>> I find it's less than productive for finding solutions to problems the
>> wiki is currently advising to leave unresolved (such as this), or
>> ambiguous (like primary vs trunk vs motorway in the US).
> It doesn't tell you to leave the problem unsolved. It only tells you that tagging the legal default if there is nothing on the ground is not the correct solution to the problem.

In the case that I was thinking of - speed limits, parking
restrictions, and right-turn-on-red-light restrictions, there is at
least something on the ground - there are signs on all the roads
coming into the town or city announcing that the speed limit is 30 mph
except as posted, that right turns on red lights are forbidden except
as posted, that parking is forbidden on all streets from midnight to
0600 after a four-inch snowfall.

There is nothing at the specific red light that has the default
restriction. There is nothing on the specific road that has the
default speed limit. There is no signage on individual roads warning
about not parking when the snowplows must operate. But there surely is
something verifiable on the ground - because the signage does appear
at the borders.

It is true that our current tagging schema cannot handle the case.
Saying "there is nothing on the ground" is less than accurate - and
feels like an excuse to avoid the discussion of travel restrictions
that apply to areas rather than individual ways.

Allowing tagging of this sort of rule on areas - perhaps requiring
that they be relations of a particular type, or that the polygon or
multipolygon have a specific tag - is actually a nearly-complete
solution. Geometric intersection of ways with (multi-)polygons in
order to determine the default restrictions is something that's
readily done. Possibly the only real sticking point would be coming up
with the set of rules to resolve conflicts if two containing areas
specify inconsistent rules.

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