[Tagging] Another reset on roundabouts

[Volker Schmidt]

At the risk that we are going in circles on this argument.

Let us try to figure out what the needs are.

What we have (in theory) at present is

   -

   a roundabout is a road layout where traffic goes around a central
   island. At present a roundabout needs to be drawn as a circular way, not as
   a node.

   The direction of traffic depends on the country (left-hand or right-hand
   drive)
   -

   a mini-roundabout is a road layout where traffic goes around a central
   traversable area. This is to allow long vehicle to use it.
   A mini-roundabout is inserted as a node, not a way.

The distinction between the two types of roundabout is clear-cut in some
countries, where there are different rood signs for the two types, and is
less clear-cut in others where the same road sign are used for both, only
the physical implementation is different.

Where does our problem stem from?

Many mappers have used the mini-roundabout node for physically small
roundabouts with an non-traversable centre island. In some cases (I have
done it myself) it has been used to mark even a larger roundabout in a
provisional way.

What we are missing in this scheme is most obviously a “roundabout” node.

Let's look at the new roundabout node:

We should give it parameter to indicate its size, for example est_diameter.

Now we have to consider the routing: If we look at the end product we want
be able to deliver, i.e. the vocal instructions, they would have to
distinguish between two categories of roundabouts:

   -

   “small” roundabouts, i.e. mini-roundabouts and roundabout nodes with
   est_diameter less than 12 meters (tbd): “turn left”, “turn right” etc
   -

   “large” roundabouts that are drawn as circular ways and node-roundabouts
   with est_diameter over 12 meters (tbd): “enter roundabout”, “take third
   exit” etc.

So, if we look at it from the routing point of view it looks to me that we
do not need to distinguish between a mini-roundabout and a small
roundabout, but what we seem to need is a way to indicate the size of the
roundabout in order to distinguish the routing behaviour.

What I am arriving at is that we need a new node “roundabout” with a
mandatory size parameter of some kind. The distinction between the present
“mini_roundabout” and a small roundabout would no longer be relevant.

Volker
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