[OSM-talk] Directional tagging

[Sven Rautenberg]

Martin Norbäck wrote:
> Hi everybody,
> I'm sure this has been discussed in length before, but I cannot seem
> to find a good way to search the archives. Anyway, I will present my
> thoughts here and you can respond or be quiet :)
> 
> I'm trying to fix at least two issues I have.
> 
> a) A way that is sort of one-way but allows buses and taxis in the
> opposite direction.
> 
> Don't know how to tag them, currently I've just ignored buses and
> taxis and tagged them oneway=yes.

To my knowledge, there is currently no official way to tag
direction-dependant (and no way to tag things on a specific side of the
way as well).

Every discussion in the past showed that there is no trivial way to do
it, and as it will heavily affect future tagging, any attempt to solve
this problem should be well thought and planned. At least I think that
is what has prevented any implementation of such tagging.

> b) 2+1 ways as we call them in Sweden, they are normal ways but have a
> small fence in the middle and 2 lanes on one side and 1 lane on the
> other side. They look like this:
> http://www.vv.se/filer/Vägprojekt/3-Falt.jpg

In Germany we have come to the agreement that if you have an object "one
street", but the two driving directions are separated in such a way that
you cannot simply (although maybe illegally) choose any lane with your
vehicle, because there is some kind of obstacle - like your fence - then
this street is tagged as two single ways, having oneway=yes set
appropriately, and maybe have a proper lanes-tag set as well. For you it
would be lanes=2 for the double way, and lanes=1 for the single way.

Regarding obstacles: Your fence is clearly an obstacle for almost any
vehicle, similar obstacles are any other form of vertical separation,
like walls. But even grass islands in the middle of the two ways qualify
as obstacle, even though they may be passed by bike or by foot, or even
by car. Motorways which only have a small patch of grass between the two
asphalt lanes should rather be tagged as two independent ways, with
appropriate tagging for the land between them, if you like.

> Now, I want a good way to tag them, and using lanes, you can maybe say
> lanes=3, or lanes=2+1, lanes=2,1, lanes=1+2, lanes=1,2, ... but how to
> interpret that. I'd rather not resort to mapping these as two ways, as
> they are in effect one way, just preventing head on collision. They
> have crossings like a normal road, no ramps, acceleration fields, etc.

Tagging it as two ways clearly state that you cannot turn around at
will, but have to drive on until you reach a crossing. Routing software
should be able to use this information.

Just have a look at German Autobahn: This almost always is only one wide
band of asphalt, but is tagged as two ways with oneway=yes, just because
this form of road has special traffic rules regarding turning
(disallowed! ;) ).


Regards,
Sven