I am learning OSM to determine if it will support a new safety/planning application.
We need polygons with rules for all street features such as a left turn lane, a crosswalk, or an intersection.
I know how for a left turn only lane ingress to an intersection, OSM can specify the length of the way segment between two nodes, the lane width, which lane changes are allowed, what kinds of vehicles are allowed, how fast they can move, and that egress from the front must be left turn.
The segment length and lane width are insufficient for non-rectangular polygons and don’t accurately geo-position the polygon. Is there an approved method of associating a polygon with this left turn lane?
Can the method be used widely with medians, sidewalks, and other surfaces?
This seems to me to be orthogonal to the use of ways that roughly indicate road centres. Is this a correct view or are there examples where both ways and areas have been used together?
Are the some examples of the area method used that I can look at in JOSM?
You can contact Marek Kleciak, he is on of the people behind the area:highway proposal.
You can find more information about it, in this interview with him.
There are quite a few highways as areas in Poland (try Warsaw http://overpass-turbo.eu/s/uoU) and somewhere there is a visualisation showing them overlaid on a conventional render. However, I think that in general lane information should remain on the linear way (the centre line), unless you want to draw individual lanes, in which case Marek will be the person to talk to.
I am not familiar with overpass. I see the map view and data view buttons. When I click the data view I get “no data loaded yet”.
Before I spend the time to learn overpass so that I can see the data. Will I see separate way/node features and area features, or are they unified?
In OSM, nodes, ways and relations are different objects. There is no concept of area (unlike what the iD editor lets you believe). We do have closed ways to represent areas. As for streets, most people map them as linear features, so a way with tags.
Only in a few limited cases (such as in Poland), people will tag highways as areas, but still the the main features for navigation (street name, highways ref, max. speed, number of lanes, turn:lanes, destinations, etc) will be mapped on the way (aka line). The area features are there to show the width of the road and perhaps some obstacles. I guess it is even more common to have a width tag on the way than having a closed way representing the extend of a road.
With Overpass you can retrieve all the above data. There is also a “function” called centroid that returns a node for all ways, closed ways and areas.
Merging data like you want, is always something that the data consumer (thus you) have to do. OSM is raw data. You can take that literally, you have to do (sometimes a lot of) preprocessing to get it in the form that you need.
In conclusion: OSM does not have the polygons you are looking for. We do have a lot of information about streets though.