OpenStreetMap
‘Le Passage du Gois’ is mostly under water. During spring tide it can be used from 1:45 before to 1:45 after ebb. At neap tide or bad weather, the recommendenation is only to cross exactly at ebb.
IMO, it is more a touristic attraction than a serious road.
How should this be designated? Tertiary road sounds too important and will draw navigation systems towards it (could be dangerous at night, as there is no barrier, just warning signs).
Discussion
Comment from spark on 21 August 2012 at 20:32
I tagged this way as causeway=yes, tidal=yes. At the time, I couldn’t find any established system for tagging these types of roads.
Comment from Zverik on 22 August 2012 at 06:54
ford=yes probably
Comment from Vincent de Phily on 22 August 2012 at 09:41
Definitely ford=yes and tidal=yes. The former is usually shown on maps and probably avoided by most router configs.
I’m tempted by some access tag, but usual time-based ones won’t do. There’s one use of access:tide=yes in taginfo but it doesn’t make much sense to me. access:high_tide=no or access:tide= sound better. You could always add an access=limited or access=tidal; most routing engines will not know what to do with the value, and simply avoid the road.
As for your actual question of the highway= value, just tag as if it weren’t tidal (the other tags already defined that). From the look of it and the tagging guidelines for France, I’d go with tertiary.
Oh… and this is not a waterway (as currently tagged). Waterways are for boats and such.
Comment from chillly on 22 August 2012 at 11:26
A ford is something you can drive or wade through - the water only covers the road by a few cms. If the road is impassible yet it is marked as a ford this is badly misleading.
Comment from Vincent de Phily on 22 August 2012 at 14:32
By your description, this road is indeed a ford, if only for a few hours each day. Even fords on rivers depend on the amount of water currently present (some riverbeds go from completely dry to flood-like during the season or because of a dam). The timescale is different but it’s the same issue. What counts as “passable” also depends a lot on your vehicle.
All in all there’s no hard rule, but if you can cross it under some circumstances, I’d say it’s a ford.
Comment from jutezak on 22 August 2012 at 19:28
Well, with flood it has a few meters of water, so the only vehicle applicable will be a boat ;)
I’m going for ford=yes, access=tidal, and downgrade it to highway=unclassified. The downgrade because it is not really for normal traffic; there is a much better bridge nearby that is not slippery and a lot wider.
Causeway does not seem to be the right tag; that seems to be a road on a kind of dyke or a road on poles like a low bridge that is too low to pass under, like the road connecting Venice to the mainland.
Comment from marscot on 24 August 2012 at 13:38
I have drove on this road its a tidal causeway. causeway=yes, access=tidal, lit=no highway=unclassified, but highway=track + tracktype=grade1 maybe be the best way to tag the road type.
Comment from jutezak on 24 August 2012 at 15:29
Hmmm… as highway=track it renders dotted. Changed it anyway. Maybe someone can chime in whether this road is actually useful for non-local car traffic (I doubt it).
I also note that the road is tagged psv=yes. That seems to mean ‘to ordinary traffic can pass here’ - which does not seem true.
Comment from marscot on 24 August 2012 at 16:39
here is a link to see theTour de France Crossing the road that day I was there.