[Tagging] Proper Tag for Not-a-Roundabout

[Tom Pfeifer]

On 08.11.2016 11:58, Dave F wrote:
> Why would you want it to "issue special instructions"? Are you askingus to add a 'this is not a roundabout' tag to fool OSRM into thinking 
it's a roundabout?

This is exactly the question we need to ask first, what should the
driver experience be?

For a small installation, which Daniel called "Roundabout Intersection", 
which a driver can overview easily from the entrance point, giving the 
exit count might be useful.

For large ones, independently if they are formally a roundabout or a 
traffic circle, this becomes increasingly difficult with the complexity 
of the road layout.

Look at Grosser Stern with its 5 main arms, each consisting of a dual 
carriageway. "Not-a-roundabout" situation.
http://www.openstreetmap.org/?mlat=52.51451&mlon=13.35013#map=18/52.51451/13.35012

When you give the 4th exit in turn instructions, the driver would need 
to carefully count the outgoing roads only, not the incoming. Try to 
distinguish them while you are in the inner lane in the circle, 
focussing on the lane markings and watching cars cutting in in front of you!

Next, check Ernst-Reuter-Platz, which is a true roundabout from the 
priority rule.
http://www.openstreetmap.org/?mlat=52.51261&mlon=13.32183#map=18/52.51261/13.32183

Slightly smaller, but the exits shaped even more into forks.

A solution could probably to improve the destination tagging on the 
outgoing roads in sync with the directional signposts, so the 
instructions can be "fork into Marchstraße towards Wedding".

> Looking at your first routing example, I'm failing to understand
> what the problem is. As it's not a roundabout OSMR appears to be give
> clear accurate information.

(Bersarinplatz) With the oval shape of the installation, the
instructions read fine, as the driver on the B96a has little "roundabout
feeling".

> I believe your second example is a roundabout

(Kottbusser Tor) No, it is not. It has neither the blue signposting, nor
has it the priority regulation of a roundabout.
Counting exits would be difficult for the driver here, as said.