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Plugin under development by User:Gorm. Gradually expands a roundabout from a single node to a full fledged roundabout.


The plugin is found in the JOSM Plugin Manager ; It's short name is REX.


  • Select a candidate for expanding. It can be a single node crossroad or an existing roundabout.
  • Press Ctrl-Shift-R or select from menu: More Tools -> Roundabout Expander
  • For each repeated press of the shortcut, the tagging and geometry will be improved towards a full roundabout with flares.


With a single node at an intersection selected:

  • The node is tagged as mini roundabout

With a mini roundabout selected:

  • The node is 'expanded' to a circle tagged as roundabout.

With a roundabout selected:

  • Convert incoming ways into flares

If no obstacles, three presses of the shortcut will create a full roundabout from a simple crossroad. The staged approach is so that one can easily correct various obstacles, improve geometry etc before continuing to the next stage. This approach also makes it easy to improve on existing roundabouts.



The diameter of the created roundabout, in meters, is determined by preference rex.circle_diameter_meter, default 12. It can be overridden by diameter=12 on the mini_roundabout.

Gap in filler nodes

To make the circle look nice, the shape of the incoming ways are conserved. Then extra nodes is put in between the way nodes. The maximum angular distance between the filler nodes is determined by rex.max_gap_degrees, default 30.


Direction (clockwise/counter clockwise) is determined by preference mappaint.lefthandtraffic. It can be overridden by direction=clockwise on the mini_roundabout.


  • Creates a smooth circle as the new roundabout
  • Copies tags from most prominent highway
  • Preserves direction of incoming ways
  • Makes flares on incoming ways

Known issues

Still in alpha version, so there is a number of smaller bugs.

Please submit issues to


Source is kept on

It was originally modelled on JOSM/Plugins/utilsplugin2 in the hope that it will one day be included in that project.