On a roundabound, how big is the area:highway=central_island, does this include the area:highway=apron , or only the inner part?
And on other places, there is a white line.
Must there be a access tag on the apron? Does the white line make any difference?
Should we tag kerbs, what type and where?
First of all, neither of them are standard
=central_island : Simply overlaps =traffic_island , and it being center could be an attribute traffic_island=centre , no need for another feature. Almost are all bulk added in Netherlands.=apron : It would be better to consider whether it’s a traversable part of a =traffic_island first (or even a =shoulder )Fundamentally area:highway= has a functional vs physical problem. Eg if an island has a walkway, it’s unclear whether the area:highway=footway should cut out the =traffic_island , or be inside it.
The other problem with this is whether areas should overlap. Conceptually, area:highway= is a roadway area. But
area:highway=bus_stop is only a part on itarea:highway=bus even tries draw lane area (which isn’t suitable to be together with =motorway etc the whole roadway to me).For the post, another comparison may be made with =shoulder for the above mention. If area:highway= =motorway etc means carriageways (US MUTCD technical term “traveled way”), it shouldn’t include =shoulder , as it doesn’t mean the whole paved roadway area (UK DMRB really simply calls it the “paved width”) . However, this is how it was suggested by one of the proposals.
Therefore this question can’t be answered without defining and standardizing what and how area:highway= should be used for. Answering it for individual features is futile.
The problem is documented as the 1st item in wiki Key:area:highway - OpenStreetMap Wiki
With all that’s said, one possible option to consider is with an attribute eg apron= similar to sidewalk:*=separate on lines, to accommodate different level-of-detail, and explicitly define what’s drawn
area:highway=traffic_island + apron=yes : When the polygon includes the apronarea:highway=traffic_island + apron=separate : When another area:highway= is drawn for the apron, limiting this object to the non-traversable partThe ‘traversable area’ is designed to be there for longer vehicles like trucks and buses, whose rear wheels follow a tighter track than the front wheels, while at the same time slowing down smaller vehicles going through the cuvre. So it is part of the roadway. Its just that part of the roadway isn’t quite as accessible to smaller vehicles. It is not a traffic island. The kerb and grass are the traffic island.
If in doubt, ask yourself the question “If I was a pedestrian, would I feel safe standing here?”
In Ireland, we tend to only have the traversable area on smaller roundabouts like this: Mapillary - in this case because it is on a bus route and the buses would have occasional difficulty making the turn from westbound to northbound. They could have chosen a mini-roundabout here, but cars would ignore it.
Aside: I have seen something similar to the traversable area in some non-roundabout locations - on a small number of turns in housing estates, where the likes of bin trucks, fire bridge, etc. might otherwise have difficult taking the curve, but it is imperative to slow down cars.
My interpretation: the traffic_island is only the inner part. The traversable part is a shoulder to the highway and can be tagged as such - as shoulder:left on the way and if desired also using area:highway.
Wait, are you suggesting to use the road’s area:highway=trunk etc?
Many aprons do have lower kerbing, and are raised at a higher level. Not the safest, but safer. On refuge islands, the highest parts which would be considered the whole or inside of a =traffic_island are quite safe, but no one usually walk or stand on them, only the =footway polygon.
And indeed, what about =mini_roundabout , no =traffic_island ?
At least in many documents, aprons can be referred to as part of islands
So ok, functionally it may not be part of an island. But physically in terms of the anatomy of a road, it could be called that. That’s why the use of area:highway= in general needs to be agreed on overall, or it could be further split into at least 2 (related to allowing various LoD) categories.
Anyway, other options not specific to the “apron” terminology on roundabouts could be the =buffer already needed to replace the meaningless =emergency; or eg =overrun
Further look at area:highway=shoulder does raise a great question: Are hatched sections of shoulders area:highway=shoulder ? Again same problem, functionally vehicles are usually not supposed to stop on them when possible, but physically those are marked on shoulders. ( road_marking=restriction doesn’t solve what it is, as hatching can occur anywhere, around the centerline, or on edges that aren’t shoulders)
Is this tag defined somewhere? I didn’t find something in the Wiki.
One of the original proposals has it, and proposed it to be inside the area:highway=motorway etc roadway Proposal:Street area - OpenStreetMap Wiki
I initially disagree with mapping that, as highway=shoulder is not a linear feature, it should not go in the value of area:highway without consideration for the exception we are making there.
If it lays in the landuse=highway, a polygon gets the key?
There’s no difference currently. area:highway=traffic_island has no highway=traffic_island either. Same for =emergency / =prohibited for what exceeds 10k and 1k. =bus is close to 1k. And notably =bus_bay , besides area:highway=bus_stop which have points.
It could be interpreted as features originally represented on the same line, not necessarily different lines. Indeed =traffic_island is even between 2 highway=primary etc roadway lines.