I was trying to offer a universal model that would accommodate both "true" 
roundabouts and mini-roundabouts.
 
In the UK you are expected to make an effort to drive around the "dustbin lid" 
(painted circle) in the middle of the mini-roundabout, but that only makes 
sense for smaller vehicles. Larger things just drive straight over it of course.
 
I disagree that a truck driver is really not supposed to use what you call the 
Truck Apron. It is simply unavoidable for anything longer than a car. Better to 
use the inner ring than to go over the outer kerb trying to avoid it. That's 
what it's there for. In law it depends on whether you consider it part of the 
"rijbaan" or not, and opinions are divided on this. There are however many 
reasons for pushing traffic towards the outside of the circle, including 
regulating the speed, minimising overtaking and improving sight lines.
 
Modelling "turbo-roundabouts" (a real Dutch speciality) is a whole different 
can of worms.
 
By the way, for (very) large vehicles there is a technique called Swept Path 
Analysis, which can be used to calculate whether it will "fit" and be able to 
take a junction. It needs the geometry of the junction, but of course it also 
needs to know a lot more about the vehicle itself which is way beyond OSM.
 
By the way, I live in NL and my son is a traffic policeman...
 
 

> On 29/01/2023 00:17 CET Peter Elderson <pelder...@gmail.com> wrote:
>  
>  
> Op za 28 jan. 2023 om 23:38 schreef Colin Smale <colin.sm...@xs4all.nl 
> mailto:colin.sm...@xs4all.nl>:
> 
> > A form of roundabout common in the Netherlands has an inner ring which is 
> > often distinctly coloured and slightly raised, thus making it clear that 
> > traffic is intended to avoid it and use the outer ring, while keeping it 
> > perfectly usable by most vehicles.
> > Example: 
> > https://nl.wikipedia.org/wiki/Rotonde_(verkeer)#/media/Bestand:N746-Noordergraafsingel-Harbrinkhoek.jpg
> >     
> > 
>  
> The raised part is the truck apron. Traffic, including trucks, is not 
> dsupposed to use the truck apron. The kerb and the raised part warn the 
> trucker who forgets that.
> The roundabout shown there is a true roundabout. Mini-roundabouts do not 
> exist in Nederland, but we do have fake roundabouts (dot or circle in the 
> middle, possibly raised, no kerb, no roundabout rules. 
> Come to mention it, true roundabouts by themselves do not have special 
> priority rules in Nederland, just the oneway rule indicated by the roundabout 
> traffic signs. However, .priority is almost always indicated by at least 
> shark's teeth. If it isn't, traffic from the right has priority, same as on 
> regular junctions. (We're driving on the right).
> 
> As for diameters, I think the (minimal) turning circle or maximal rigid 
> vehicle length is what traffic needs. I am not sure that it can be calculated 
> from the diameters of inner centre circle, outer centre circle and 
> circumference of the entire traffic area.
>  
> 
> > 
> > > On 28/01/2023 22:12 CET Philip Barnes <p...@trigpoint.me.uk 
> > > mailto:p...@trigpoint.me.uk> wrote:
> > >  
> > >  
> > > Diameter implies there is something circular. The paint is often round, 
> > > not always, but most are just former T junctions or cross-roads where 
> > > there is nothing to measure the diameter of .
> > > 
> > > Phil (trigpoint)
> > > 
> > > On 25 January 2023 17:50:54 GMT, Volker Schmidt <vosc...@gmail.com 
> > > mailto:vosc...@gmail.com> wrote:
> > > 
> > > > Is there an established way to tag the diameter of a mini-roundabout?
> > > >  
> > > > We have the tag diameter, but I could not find it applied to 
> > > > mini-roundabouts.
> > > > 
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