Converting a Stoplight intersection to a roundabout

Hello all,
I am a beginner to opensteetmap, and have a couple of questions with JOSM.
I am trying to convert a stoplight intersection (33.983031, -117.331125) into a roundabout intersection for a simulation. Canyon Crest is a 2 lane street ( 3 lanes including the left turn, and Blaine is a 4 lane street (5 lanes including left turn). I want to know 3 things:

  1. How do I split the roads into individual one way lanes?
  2. How do I create a circle in the middle with connections to the lane?
  3. How would I define this new shape as a roundabout with respect to traffic law/definitions?
    My images would not upload, so I just attached it into a google drive folder.

I have never used josm before, so I apologize for the basic questions. My goal would be to have an roundabout that is similar to the Palm Desert model I attached in the drive. If there is some additional information you need, please let me know. I will respond any questions you may have. Thank you for the help.

Welcome to OpenStreetMap!

Roundabouts = diving in with both feet! Good for you! On the plus side, by the time you know how to do everything involved in building out a proper roundabout, you’ll have a solid foundation of JOSM skills!

There is a lot of OSM info already written by many knowledgeable people. So, I’m going to point you to some specific places for answers to your questions in the hope that you get a feel for finding your own future solutions.

  1. Split way, add way, tags, oneway, turn restrictions.
  2. circle, reconnect, cleanup the mess.
  3. As for traffic law/definitions – Design-wise, that’s what Traffic Engineers do. OSM uses junction:roundabout. Here’s a roundabout design link.

Regarding your mentioned fancy-dancy round’d’round – alt select, copy , paste & rotate should get your “simulation” started. Then, for real mapping, there are relations – fun, fun!!


From looking at available imagery, the junction at:- does not look like a roundabout.

Please be very careful when using JOSM not to upload any fictional data to OSM, it is very easy to inadvertently upload. Not so easy to revert.

He is doing a simulation. Should use Discourage Upload.