[Talk-GB] traffic island mapping / harmful detail?

[Mark Goodge]

On 31/03/2021 12:30, Stephen Colebourne wrote:
> I add some areas in the middle of traffic, for pedestrians.
> 
> My rule is that I add them in association with explicit sidewalks, as
> it makes it much easier to follow the sidewalk. The classic case is
> where a pedestrian crossing is two-phase, and the pedestrian has to
> walk parallel to the road, as shown here (I hope it can be seen that
> the map is clearer for pedestrians with the island explicitly mapped):
> https://www.openstreetmap.org/#map=19/51.40863/-0.21544
> 
> I wouldn't split a road to do this though - I'd be adding it in a
> place where the road already justifies being split. For a small
> pedestrian crossing island I feel that `crossing:island=yes` is the
> best option (and I always add `crossing:island=no` too):
> https://www.openstreetmap.org/node/7259595189

I entirely agree with this. Splitting a road just to add street 
furniture is, IMO, the wrong choice. For a start, it looks odd on the 
standard user-facing map (yes, I know, don't tag for the render, 
but...), which I think is unhelpful. But, also, it goes against the way 
that roads, at least in the UK, are classified in real life.

Splitting a road creates a short (very short!) stretch of dual 
carriageway as far as the map is concerned, but as far as highway 
legislation and management are concerned the presence of an island does 
not, alone, create a dual carriageway. It only becomes a dual 
carriageway, and therefore should only be mapped as a dual carriageway, 
if there is a median between the two halves that's long enough to form a 
distinct pair of matching carriageways. The minimum length necessary to 
create this is a valid matter of debate, but I think Stephen's first 
example, above, clearly does meet those criteria whereas the presence of 
an island at the second does not.

Mark