[Tagging] Tag ref on motorway_link

[Colin Smale]

Hi Martin,

First and foremost, tags applied to an object should of course refer to
that object. I normally interpret the "ref" tag on a ROAD as "the
reference ID of that ROAD as designated by the powers-that-be". Motorway
slip roads are (in my experience in UK/NL) administratively speaking an
extra part of the motorway, which means the ref should be whatever the
authorities consider it to be part of. There are often clues to this in
the form of codes on street lights and distance posts.

On the other hand, if the ref is to be interpreted as "the road reference
for that road as present on the signs for the public" (referring to that
very road itself, not the road the ramp leads to) then the junction number
may be more appropriate. On the English wiki page for motorway_link it
kind of hints in this direction.

A "motorway exit" is really a compound object including typically four
slip roads and sometimes roundabouts etc. Puritanically speaking we could
considering modelling exits as a relation, with the motorway_links
included with role=on_ramp etc. Then the junction number would live on the
relation. A link from one motorway to another could then easily be shared
between the relations for the junctions on each motorway. (In the UK,
motorway-motorway junctions are numbered like any other junction. In NL
they are not included in the junction numbering sequence; instead they
have names like "Knooppunt Oudenrijn").

I guess the same question may be applied to the name tag?

Colin

> Hi!
>
> I'm wondering what ref should be used on slip roads/ramps of a motorway
> (not the junction node, but the way tagged with motorway_link). Up to now
> I've seen:
> * the reference of the junction
> * the reference of the motorway
> * the reference of the junction not in the ref tag but in junction:ref
> * nothing (neither ref nor junction:ref)
>
> In the Wiki (English and German) I couldn't find an answer.
>
> Any opinions/comments/hints are welcome.
>
> Thanks,
> Martin
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