[talk-au] Splitting Ways for small roundabout traffic islands

[Andrew Davidson]

On 15/11/21 22:14, Andrew Harvey wrote:
> Splitting makes the data more complicated than it needs to be, and 
> doesn't add more value or accuracy compared to simply tagging the 
> traffic island as a node. One with a gap for pedestrians gets tagged as 
> crossing:island=yes, without a crossing maybe traffic_calming=island, or 
> some other tag.

I didn't recall seeing this type of tagging, so I took another sample. 
This time 50 single carriageway roundabouts without split flares in 
BNE/SYD/MEL/ADL. After looking at 200 roundabouts I couldn't find any 
that have used traffic_calming=island to model the split. I think that 
we have a consensus that if you do model a roundabout's flares you split 
the ways, rather than tagging the island. What we don't seem to have is 
a consensus on what constitutes a "small" roundabout that doesn't need 
to have the flares modelled.

> What I'd like to hear is from those who do split, is why? Is it just 
> because you're trying to follow the documented rules, or is there a 
> reason for splitting being better? Ideally we'd document the community 
> preferred approach along with the reasons for.

Personally I spilt the ways to model the flares. The reason I do this is 
because I started mapping in CBR and that's how they are mapped here. I 
assume that is the style here because our roundabouts are larger than 
you find in other cities.

I wouldn't have thought of using traffic_calming=island as this makes me 
picture this 
https://wiki.openstreetmap.org/wiki/File:Trafficcalming-island.jpg type 
of thing. However, the wiki does suggest you can use it to model the 
roundabouts islands.

The wiki also has an example of how to map a roundabout which shows the 
ways split. There was also a JOSM plugin that semi-automated the mapping 
of a roundabout and it also split the ways for you.