[Tagging] Expressway=yes/no versus new tags "dual_carriageway=yes/no", "limited_access=", "grade_separated"=?

[Joseph Eisenberg]

I've created a page for Key:dual_carriageway based on existing usage
in the database:
https://wiki.openstreetmap.org/wiki/Key:dual_carriageway

On 2/20/20, Joseph Eisenberg <joseph.eisenberg at gmail.com> wrote:
> I updated the Key:expressway page to have a global focus, rather than
> being United-States-specific.
>
> But I noticed that the key:expressway is currently used in 2 different
> ways.
>
> While all expressways are major roads designed for high-speed motor
> vehicle traffic, they are not often "motorroad=yes", because most
> States allow motorcycles and pedestrians on all roads that are not
> motorways (and western States allow bicycles on rural motorways even).
>
> The defining characteristics are:
> 1) The max speed and design speed are relatively high (usually 60 kmh
> in urban areas or greater in rural areas)
> 2) A) They have limited access to adjacent properties
> OR
> B) They have grade-separated interchanges with major junctions.
> 3) They are dual carriageway (divided) highways
>
> While many "expressways" in the United States fit all of these
> characteristics, many only fit 2)A) or 2)B) but not both.
>
> We already have "max_speed=", but it would be better if there were
> more specific tags to describe these three properties:
>
> A) Limited access: there are no or very few service roads or driveways
> B) Grade separation: there are no stop lights or stop signs (or
> roundabouts) at junctions, instead the roads cross at different
> levels, with link roads / ramps to connect them.
> C) Dual carriagway: the two directions of travel are divided by a
> barrier or median area.
>
> So initial ideas;
>
> A) a new tag "limited_access=yes/no" - or is there a better term in
> British English for a road which doesn't have service roads like
> driveways, or only very rare intersections with service roads? This
> needs a proposal.
>
> B) Use the tag "grade_separated=yes/no" for roads that generally do
> not have any at-grade intersections with stop lights, stop signs or
> roundabouts or similar. Used only 97 times:
> https://taginfo.openstreetmap.org/keys/grade_separated so should need
> a new proposal.
>
> This property can be seen by looking at all crossing or intersecting
> roads and interpreting layer= and bridge= and tunnel= tags, but that
> is quite hard to get right, so having mappers add this tag would help
> with quality control and make it much easier for database users.
>
> C): I noticed that the tags "dual_carriageway=yes/no" and
> "type=dual_carriageway" have been used in a few limited areas. These
> have been used several thousand times
> (https://taginfo.openstreetmap.org/keys/grade_separated) but only in a
> few places, so a new proposal is still a good idea.
>
> This property is also mapped by drawing two separate ways and adding
> oneway=yes, but it is not easy for a computer algorithim to properly
> interpret these geometries as "two parts of a single road" without a
> tag like "dual_carriageway=yes", especially if there the name= and
> ref= are not identical for each direction.
>
> - Joseph Eisenberg
>