[Talk-GB] Turn Restrictions at roundabouts

[James Derrick]

Hi,

On 03/10/2020 14:05, Brian Prangle wrote:
> There seems to be a predilection for adding turn restrictions , either 
> no right rurns or no U turns at the exit flares of roundabouts to 
> prevent turning back into the entry flares where there are no explicit 
> signed restrictions. I suspect this is "rendering for routers". Do 
> routers actually need this data?  I'm tempted just to delete them all 
> wherever I meet them, but I suspect there are thousands of them and 
> there'll be howls of complaint.

About the only change I've made in years of mapping 'non-mini' 
roundabouts is to split the oneway=yes flare 'V' into two segments. JOSM 
validation started flagging the junction node of the V as too tight a 
bend, which I suppose makes sense.

I wonder if seeing a junction node of three vertices rather than a 
300degree turn on one segment make a difference to roundabout unaware 
routers?

Poor attempt at an ASCII diagram explaining what a two segment flare is 
below!

Flare 1 ->---\

               * --------Road 3 continues away from roundabout

Flare 2 -<---/

Flares are the oneway=yes roads connecting to the roundabout.
These are often a single V shaped segment, rather than two plus the road.


James
-- 
James Derrick
     lists at jamesderrick.org, Cramlington, England
     I wouldn't be a volunteer if you paid me...
     https://www.openstreetmap.org/user/James%20Derrick