Circular and widened road features

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Logo. Feature : Circular and widened road features
One example for Feature : Circular and widened road features
Description
Circular and widened road features
Tags


In OpenStreetMap we have several tags that describe different circular and widened road features. Perhaps the three tags which are most commonly confused with each other are:

Because of incomplete or ambiguous documentation, misinterpretation or just for the sake of simplicity they were often used in situations, where they do not apply. The major differences between the three are:

  • A roundabout is a one-way street with right-of-way and a non-traversable center island.
  • A mini-roundabout is a one-way street with right-of-way and a traversable center island. In particular, large vehicles are allowed to drive across the center island if otherwise not possible due to their dimensions, i.e. it might be impossible for a large vehicle to drive through a roundabout but possible to drive through a mini-roundabout with the same dimensions.
  • A turning circle is a widened space on a two-way street without any center island (or at least a fully traversable island). The absence of a center island allows also large vehicles to turn around.

Another term sometimes mistaken for a roundabout is a traffic circle: contrary to roundabouts, the entering traffic is controlled by stop signs, traffic signals, or is not formally controlled. This wikipedia article explains the difference of a roundabout and a traffic circle according to the United States traffic engineers. In OSM traffic circles are usually not indicated by specific tags.

A very common question is: "Why is it important to follow this tagging guideline if the map looks good even when tagged differently?"
The answer is: The map is not everything. There exist a lot more applications which process our data and these tags have different implications e.g. for routers. So if you tag a small roundabout as a mini-roundabout or a loop at the end of a street as a turning circle, it might look ok on the map but will break other applications. So please don't think of this as annoyance and try to use the most fitting tags in each situation.

The following table presents the preferred tagging for the most common situations and also tries to clarify some ambiguities.

Photo Tagging Remarks
San Agustin Roundabout A.jpg Closed way
highway=*
junction=roundabout
A standard roundabout with a large, non-traversable center island.
Mini-roundabout Duckpool Road, Newport - geograph.org.uk - 1435594.jpg Closed way
highway=*
junction=roundabout


or alternatively

Node
junction=roundabout
direction=clockwise

Small, but not a mini-roundabout. Although it is preferred to tag this the same way as a large roundabout, for the sake of simplicity it is acceptable to tag this with a single node with junction=roundabout. In this case the tag direction=* should be specified, as its default value is anti-clockwise when used in conjunction with a roundabout.
Mini-roundabout in Staining - geograph.org.uk - 1394614.jpg Node
highway=mini_roundabout
direction=clockwise
A classical mini-roundabout where the center is only a painted circle. The tag direction=* should be specified, as its default value is anti-clockwise when used in conjunction with a mini-roundabout.
Erfurts famous miniroundabout 2.jpg Node
highway=mini_roundabout
Large, but a mini-roundabout. The center island is traversable and without signposts.
Kreisverkehr.jpg Node
highway=mini_roundabout
Also a classical mini-roundabout with a slightly raised but still fully traversable center island.
Turning circle, Temple - geograph.org.uk - 1537665.jpg Node
highway=turning_circle


or alternatively

Area
highway=*
area=yes

This photo shows a round place with a traversable island in the middle, but this is neither a mini-roundabout nor a roundabout, but instead a turning circle, which allows large vehicles to turn around. Please bear in mind that a turning circle can have any shape, but never a non-traversable island.
Junction with central island.jpg Node
traffic_calming=island
Don't let the island confuse you: there are indications neither of a one-way nor of right-of-way, so this is just a junction with an island used for traffic calming.
Kein kreisel IMGP9185 osm.jpg Node
traffic_calming=island
Watch the arrows closely - this is also just a junction with traffic calming.
Turning circle - geograph.org.uk - 991834.jpg Closed way
highway=*


or alternatively proposed

Node
highway=turning_loop

Obviously a place for vehicles to turn around. But because of the island, it is not a turning circle (which must not have an island), so this should be mapped as a loop. For the sake of simplicity the tag highway=turning_loop on a single node is currently under discussion.