[OSM-talk] [Tagging] - RFC - Motorway_linkimpliesoneway=??

Dermot McNally dermotm at gmail.com
Tue Oct 7 13:41:58 BST 2008


2008/10/7 Ed Loach <ed at loach.me.uk>:

> This is a roundabout where you can go either way around the "big"
> roundabout, and at each junction with a road there is a
> mini-roundabout. When these sort of roundabouts, often nicknamed
> "Magic Roundabouts"
> http://en.wikipedia.org/wiki/Magic_Roundabout_(Hemel_Hempstead)
> cropped up on this other email list I wondered how they were tagged
> in OSM, because of the implied oneway of junction=roundabout.

http://www.openstreetmap.org/?lat=51.562812&lon=-1.77143&zoom=18&layers=B000FTF

This is the original Magic Roundabout in Swindon. Here, some licence
has been taken with the ways, as you'll see that the "two-way" nature
of the flow is implemented here as separate one-way ways. On some
sections, this is accurate, as there are real traffic islands. In
others, there is just hatching, but since you may not cross it, it's
not the biggest tagging sin imaginable. Strictly speaking, the
mini-roundabouts should be tagged as such, but I can imagine that
would be difficult to do nicely given the dual ways that would
converge at each one.

Road geeks would contend that Magic Roundabouts are not really
roundabouts (apart from the outer minis), but "gyratory traffic
systems". The distinction being that they diverge from standard
roundabout rules of flow, right-of-way, layout etc., but are still
circular. The API seems to be antisocial at the moment, so I can't
check the tagging, but my inclination here would be not to tag
anything but the 5 outer roundabouts with junction=roundabout. Think
of what a routing application might make of it...

Dermot

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