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

[Colin Smale]

This is fine for straight-across crossings with a simple island. What about a longer island, with staggered crossings, and independent traffic lights for the two halves? It may be only elongated by a couple of metres, but topologically speaking (relevant for routers/navigators, and don't forget the pedestrian's viewpoint is different to the driver's) very different. Maybe in this case it would be correct to split the way around the island. If so, what makes the difference? The stagger? The lights?

> On 03/31/2021 1:54 PM Mark Goodge <mark at good-stuff.co.uk> wrote:
> 
>  
> 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
> 
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