Tag:junction=roundabout

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Public-images-osm logo.svg junction = roundabout
Kreisverkehr2.jpg
Description
A road junction where the traffic goes around a non-traversable island and has right of way.
Used on these elements
may be used on nodes
may be used on ways
should not be used on areas
use on relations unspecified
Useful combination
Implies
Status: Unspecified

A Wikipedia roundabout is a road junction where the traffic goes around a non-traversable island (or a void in case of elevated roads) in the middle, and the traffic on the roundabout has right of way. Roundabouts can have any size from tiny to huge with several lanes.

Please pay attention to the section “Possible misinterpretations” to differentiate between roundabouts, mini-roundabouts, turning circles and further road features.

How to map

Start by drawing a circular shape, which would represent the roundabout. Furthermore:

  • The OSM ways of the roundabout itself must be drawn in the direction the traffic flows.
  • Tag the OSM way(s) of the roundabout with junction=roundabout.
  • oneway=yes is implied, but can be added for clarity.
  • Connect it with the roads approaching the roundabout. If a road is split into two separated carriageways (one approaching, one departing), draw those explicitly and tag these carriageways (not the roundabout) with oneway=yes. Pay attention to their correct orientation and use separate nodes of the roundabout for the approaching and departing road.
  • Also tag the way(s) with highway=*, the same as the connecting roads. If there are several roads of different importance connecting to the roundabout, you should usually use the one with the greatest importance, that does not begin/end at the roundabout.
  • A roundabout should only be tagged with name=* if the junction itself is named independently and differently from the roads crossing it.
  • Each road has to be connected with the roundabout in a separate node, i.e. between these nodes a segment of the roundabout is required. Thus routers can safely recognise that a section of the roundabout has to be driven through.

Editor support for circles

JOSM

There exist two ways to draw a circle in JOSM:

  • Draw a closed way and press the key 'o' or select Tools -> Align Nodes in a Circle in the menu
  • Select two or three nodes (e.g. ending nodes of ways leading to a roundabout) and press 'shift-o' or select Tools -> Create Circle in the menu

Potlatch 2

In Potlatch 2, draw a closed way with at least three nodes and use Align in a Circle in the toolbar.

iD

In iD, first draw a closed way. Then select the way and press the key 'o', or select the way and click the button that has an image of a closed way on it (labeled "Make this line circular" when you hover over it) in the curved grey contextual menu.

Examples

Signposts

Roundabouts are usually indicated by signposts, like e.g. one of these:

Roundabout sign Israel.png Mini roundabout sign.png Diamond road sign roundabout.svg Australian Roundabout warning sign.png CZ traffic mark C1 roundabout.svg Singapore Road Signs - Warning Sign - Roundabout.svg Square in Iran.png Znak A-8.svg

For larger roundabouts, sometimes different signage is used (e.g. plain yield signs). As long as the main principle - the traffic on the roundabout has right of way - is maintained, this is acceptable for tagging as a roundabout.

Roundabouts

The following table shows a selection of classical roundabouts: they all are one-ways with a non-traversable center island, and the traffic within the roundabout has right-of-way. For the determination of the correct highway=* see the next section.

Kreisverkehr2.jpg Hamilton Roundabout.JPG San Agustin Roundabout A.jpg
New Roundabout - geograph.org.uk - 786383.jpg highway=*
junction=roundabout
Roundabout denmark 0075.jpg
Blackwood roundabout.jpg Mini-roundabout Duckpool Road, Newport - geograph.org.uk - 1435594.jpg Lau Fau Shan Roundabout 2012.JPG

Selection of the right highway tag

The following examples focus on the determination of the correct highway=* for the roundabout and therefore only this tag is listed. When tagging a roundabout, junction=roundabout always has to be specified.

Image Highway tag Assumption Description
Mapping-Features-Roundabout-Double-Carriageway.png highway=trunk A dual carriageway trunk passes through the roundabout with two unclassified roads also connecting to it. The trunk which passes through the roundabout has the highest importance, and therefore the roundabout itself should also be tagged as trunk. Also use two nodes on each side to connect the trunk to the roundabout - one for each driving direction.
Mapping-Features-Roundabout-Secondary-Ends.png highway=unclassified A secondary road ends at the roundabout, the other three roads are all unclassified. The secondary road has the highest importance, but it ends at the roundabout. The unclassified roads pass through the roundabout and therefore the roundabout is also tagged as unclassified.
Roundabout-Primary and Secondary.png highway=primary A primary road connecting from north and west, a secondary road ending east and a service road ending south. The primary road has the highest importance and does not end at the roundabout. Therefore the roundabout is tagged as primary.

Possible misinterpretations

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.


Signal-controlled Roundabouts

Many roundabouts with heavy traffic are modified with traffic signals controlling traffic on the roundabout itself. Traffic joining the roundabout may not have to obey standard rules of priority at some entrances to the roundabout because of the signalling. In many cases some entry roads (those with lighter traffic) on these roundabouts are not signal controlled so that the whole junction still behaves as a roundabout (e.g., http://osm.org/go/eu5aUXR98--). Even when all junctions are signal-controlled, it is suggested that junction=roundabout be retained.

Not a roundabout

Strausberger Platz Berlin Vorfahrt.jpg

It is not a roundabout if one of the roads entering the circle has the right-of-way. In this situation the tag junction=roundabout has to be avoided. In addition, the major and minor road should intersect in one node only, typically in an acute angle. An example is the Strausberger Platz in Berlin, Germany.

In spite of their name, Hamburger roundabouts (http://en.wikipedia.org/wiki/Roundabout#Hamburger_roundabout), also known as throughabout or cut-through, are not roundabouts. In this situation the tag junction=roundabout has to be avoided strictly.

In all these cases, the key “junction” is not necessary at all. You need no special tagging.

Related tags

See also