# Re: [Routing] Roundabouts - why is a separate segment required?

```What you describe is a mini-roundabout.
That has a different geometry as the center of that one is traversable.
```
a)
I don't see a node as anything you "are on" at any time. Only segments.
```
At most nodes are considered for calculating the metric of making certain turns
```between segments.
b)
```
Routing algorithms that don't know or deal with roundabouts would still work
```perfectly well with a circle of segments and give proper instructions.
c)
```
In reality this is a circle of road-segments. So segments represent reality more closely. So for the purpose of the map as a representation of real world geometry, this is simply a much better approximation. This is not only for routing but also for map-rendering to scale the size of the roundabout correctly. (There are vast differences in possible sizes.)
```d)
```
These segments have a significantly different metric then an intersection (much slower traffic
```in the roundabout then the surrounding roads).
```
They have an angle to the entering and exiting road that can be used in a metric because you need to slow down to make such hard turns, limiting your average speed in the segments before and
```after the roundabout (lookahead).
```
There may be traffic jams or construction sites blocking part of a roundabout but still allowing certain turns to be made. This can not be described with a simple node.
```

On 2018-02-14 15:40, Dave F wrote:
```
```Hi
Could anyone give me an explanation for this line from

"Each road has to be connected with the roundabout in a separate
nodeâ€”that is, between these nodes a segment of the roundabout is
required."

I see no requirement for a separate segment:

* When a entering road shares a node with a roundabout then the
router knows it's entered that roundabout by reading the tags on the
circular way.
* Whilst on that node, the router checks to see if there are any
suitable exits. If there are, then it leaves the roundabout.
* If not, it continues going around until it finds an appropriate
exit.

Cheers
DaveF
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```
```
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```