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 nodesmay be used on waysshould not be used on areasshould not be used on relations
Implies
Useful combination
Wikidata
Status: in use

A roundabout is a generally circular (self-intersecting) road junction where the traffic on the roundabout has right of way.

The tag junction=roundabout is used only on road intersections where traffic on the roundabout has right of way.

That is, the roundabout itself should be free from all intersection controls including traffic signals, stop signs or stop markings, give-way (or yield) signs or give-way markings. However there exists exceptions in some roundabouts in some cases where there's a special service way passing through the island, reserved to buses/tramways/emergency vehicles (which will have priority to the normal traffic, and for which there may be traffic signs requiring vehicles on the ring to give the way; in normal times these giveways and traffic signals are off).

Where traffic does not have right of way, this is a rotary (also called traffic circle). The tag junction=circular should be used on rotaries.

The size of a roundabout can vary from small to very large with several lanes.

Naming

Only if the roundabout itself has a name should the name=* key be applied (such as John's Junction).

Except for this very uncommon circumstance a junction=roundabout should not have a name=* tag.

Older fixme=name errors for roundabouts can be ignored and removed.

Ways connecting to the roundabout

All ways which intersect with the junction=roundabout should be connected to a separate node.

Ways which enter and exit a roundabout should never connect to the same node on the roundabout.

This is required to allow routing applications and software to provide correct directions, otherwise the routing software will not correctly recognise the roundabout, or that it is a junction.

Misclassification

Please pay attention to the section “Possible misinterpretations” to differentiate between:

  • Roundabouts (junction=roundabout)—where traffic on the roundabout has right of way;
  • Rotaries and traffic-circles (junction=circular)—where traffic on the rotary does not have right of way;
  • Mini roundabouts (highway=mini_roundabout)—used only on nodes, as a roundabout where the centre of the roundabout must be traversable;
  • Turning circles (highway=turning_circle)—used only on nodes, including cul-de-sacs; and
  • Turning loops (highway=turning_loop)—used only on nodes, where a road island or similar feature is present.

How to map

Short tutorial showing how to draw a roundabout using the iD editor (click on image to start animation).

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.
  • Give it a name only if is official or displayed (generally it is different from the name of highways connecting or passing though them, but many of them remain unnamed as it is undecidable between these competing highays, and because there's no address for residents located inside, or because addresses are given to one of the connecting highways: only large roundabouts have a dedicated name).
  • oneway=yes is implied and redundant. Though it is not wrong to add it explicitly, it is not needed. However it may be useful to tag the number of lanes=* in the ring (typically 2, where long vehicles will need to use both; 1-lane roundabouts are especially important to tag if they exist for large, but usually roundabouts the second lane, or are transformed to miniroundabouts whose central island is not blocking but can be used at very slow speed by long vehicles).
  • 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. You may also tag nodes where vehicles stop to give way to vehicles already driving in the ring.
  • Also tag the roundabout and approaches 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. Tagging the number of lanes=* (typically only one in many roundabouts) on one-way approaches will be useful.
  • Again, 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—that is, 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. You should always be able to trace it; if not, that's because you did not trace the roundabout within its most external lane where vehicles can enter and exit the roundabout and should increase its radius a bit more by moving nodes on interconnection nodes and using the "make circle" tool in your editor to regularise it.
  • You may optionally trace the central island itself, if the roundabout is large enough, notably if it is bordered by barriers or kerbs, or if it includes significant features such as trees or decorating plants, or a fountain or monument.

Roundabout-tagging.png

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

There is also the JOSM/Plugins/RoundaboutExpander that can help you draw a roundabout in just a few clicks/shortcut presses.

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:

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.

For larger roundabouts, multiple signs may be used: as a prior alert (frequently with speed limit signposts) along highways before entering the disjunction area, just at end of highways where a giveway priority must take place (with sign posts and/or painted marks on the floor through the highway, and on the traffic island itself. Additional signs on the central islands (possibly with flashing lights) may also explicitly signal the required change of direction and will help detect the island from longer distance to reduce the risks of collisions. As well directional postsigns may indicate the only oneway directions to follow at end of highways (generally oblique arrows pointing down to the mandatory lane), where lanes are diverging, to signal the presence of a separator island.

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.

The major differences between the four are:

  • A roundabout is a one-way street with right-of-way and a non-traversable centre island. There can be traffic light, as long as the circular road has right-of-way when the lights are off.
  • A mini-roundabout is a one-way street with right-of-way and a traversable centre island. In particular, large vehicles are allowed to drive across the centre 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 circular junction is a one-way street around a non-traversable centre island, however the circular traffic has not always the right-of-way, it has to yield at some or all incoming roads. This includes traffic circles with such yield regulations as perceived in the United States.
  • A turning circle is a widened space on a two-way street without any centre island (or at least a fully traversable island). The absence of a centre island allows also large vehicles to turn around.

Why is it important to follow this tagging guideline if the map looks good even when tagged differently?
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 centre 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 centre 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 centre 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 centre island.
Grosser Stern Berlin circular traffic must yield.jpg closed way
junction=circular
Traffic routed in a circle, with a large, non-traversable centre island. However the circular traffic must yield for each entering road, thus not a roundabout.
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.


Special cases

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.

Shapes

Note also that roundabouts are not necessarily circular in shape: there does exist roundabouts that are 0-shaped (oval) or D-shaped (with a straight segment, notably those created on a square whose one side is along an avenue), or slightly 8-shaped (created by assembling two earlier nearby roundabouts, but removing/barring their median junction, which was earlier bidirectional but with their directional lanes in inverted sides compared to normal roads).

Some roundabouts also include one way lateral shortcuts (to be traced separately as normal oneway highways).

Much more rarely some roundabouts include a way crossing them in the middle (usually this way is restricted for buses or trams, with a priority for these vehicles going through this restricted way, or for footways crossing the roundbout, and give-ways barring the main loop of the roundabout to implement this priority of traffic, without placing any traffic light controls, that would no longer make them eligibible as roundabouts that can only work with priorities: if there are traffic lights blocking vehicles on the loop, you should not map any roundabout but standard crossroads and one-way highways for the loop). But most of the time (when the restricted way in the middle is not used by buses or trams, they crossroads are working as roundabouts (with only the priority given to vehicles that are already in the loop, and give-ways before entry in the loop near the end of connectings highways).

Not a roundabout

Strausberger Platz Berlin Vorfahrt.jpg

(This is invalid. Page will be updated shortly (2017-11-28) 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. Such junctions can be tagged junction=circular.

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. These cases need no specific “junction” key.

Related tags

See also

Temporary Gallery of Roundabout Diagrams

These are roundabouts. They should be tagged with junction=roundabout.

For a junction to be a roundabout all entering roads (Roads A, F, H, and K in diagram) must have a traffic-control (that gives right of way to the traffic on the self-intersecting circular road).

Where roads bisect or cross the self-intersecting circular road at grade level all these roads must also have traffic control (Bus Lane in diagram)

Traffic controls can include Give-Way (Yield) and Stop signs and road markings, and traffic-signals. All traffic control symbols depicted in the below diagram are interchangeable between eachother.

Temporary Gallery of NOT Roundabout Diagrams

These are not roundabouts. They should not be tagged with junction=roundabout. Some of these junctions should be tagged with junction=circular

Note roads A, F, H, K, M and N in diagram which do not have traffic controls.