[Tagging] Divided highways, and not so divided highways, one way or two

Florian Lohoff f at zz.de
Thu Oct 10 08:44:34 UTC 2019

On Thu, Oct 10, 2019 at 08:38:28AM +0200, Frederik Ramm wrote:
> Hi,
> DWG has been asked to mediate in a user dispute in Germany where a local
> mapper has chosen to represent a busy four-lane primary highway (two
> lanes in each direction, and a double continuous line painted in the
> middle which is physically possible but legally not allowed to cross).

I am one of those mappers - So disclaimer applies - i am tainted.

I am in favour of relaxing this rule. We currently have strips of
road where we currently handle this relaxed e.g. Motorway links or
exits where we (OSM Germany) map ~50% of the exits with completely
seperate ways although there is only a single line in the middle.

I'd like to use it for a 4 lane motorway size like road where is only
a double line in the middle. Double line means, not allowed to cross,
and additionally - no part of a vehicle may leap over the line. So 
in practice left turns are not allowed, u-turn is not allowed. And for
this specific strip foot and bicycle are disallowed and we had no speed
limit for years (Was introduced couple years back).


Mapping large, multi-lane roads with a "do not cross line" in the
middle as single line requires 4-5 times the number of turn
restrictions. These are number i am estimating from my own experience
mapping it one or the other way.
At every way junction one has to model every disallowed way/turn.
From my experience this is very error prone.

I am doing a lot of QA concerning routing (100K routes every 2 hours for
the region i am mostly interested in). From the experience doing this
the last 6 years it shows that meanwhile handling of turn restrictions is 
causing 90% of routing problems due to people unintentional breaking,
abusing, misinterpreting or overcomplicating turn restrictions.

So - in other words. I am in favour of the KISS principle. Make
it easy for the average mapper and let them handle as they seem
fit. As a rule of thumb the current handling is okay. But there
is no "one size fits all". And I'd like to relax the rules 
in favour of reduced complexity.

And i see fit in the original "Conventions" document [1] which terms
it as "Divided highways should be drawn as separate ways." for divided highways.
First - "should" is a relaxed term which is no MUST and second - 
it does not make any statement about whether we MUST draw a non physically
divided highway as one line. (I dont oppose the fact that in 99% of the
cases it makes absolute sense to do so).

[1]: https://wiki.openstreetmap.org/wiki/Editing_Standards_and_Conventions
Florian Lohoff                                                 f at zz.de
        UTF-8 Test: The 🐈 ran after a 🐁, but the 🐁 ran away
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