[Tagging] How to tag: Legally separated ways

Martin Koppenhoefer dieterdreist at gmail.com
Tue Oct 16 16:32:48 GMT 2012


2012/10/16 Chris Hill <osm at raggedred.net>:
> Perhaps in your part of the world, but not everywhere. Crossing solid lines,
> as centrelines or lane separators have exceptions for ordinary vehicles (not
> just emergency vehicles) here. Yet another example of how local influences
> must be applied to documentation. The page showing how highway types are
> interpreted in different countries may be copied for such definitions.


yes, traffic rules are different in different areas, and someone
offering routing should make himself familiar with local exceptions.
This is even more an argument to keep straight definitions. If you map
that there is no physical division but only a specific legal divider,
this information will be available to those who interpret the data
according to their rules, but if you treat all kind of divisions the
same (separating the ways in OSM) routers will asume for everybody
(pedestrians, emergency vehicles, bicycles) that there is no
connection (unless you create these connections, either  explicitly
(connecting (foot?)ways) or conceptionally by creating a relation
between the two).

When you choose to split the ways and create a relation between the
two, there will still remain some questions open. Actually you
shouldn't tag them as highways then, but as lanes, so the question is
how to deal with this.

Would you make
a) no highway at all and dataconsumers would need to take all lanes as
well in account (or maybe get single highways from preprocessing) or
they would have holes in their data.
b) assign the highway-tag only to one of the ways (actually not
working without introducing further "helper ways")
c) assign a highway-tag anway to all these lanes and additionally
state that they are lanes.
d) do nothing of this and renounce from the details.


Frankly I think that none of these alternatives with the relation is
really nice. b) would probably be the easiest to introduce, because
dataconsumers could in theory ignore the lanes and rely only on the
highways, but practically you would have to continuously fix newly
introduced holes in the graph, because of higher complexity.

The divider tag (almost not in use) could solve the problem we have in
countries where there is no exception for driveways on the opposite
side, and in general it could make mapping easier because far less
turn restrictions would be needed (if routers adopted this mapping
style).

cheers,
Martin



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