and then the Roundabout Edit Tool 
button.
With the Roundabout Edit Tool you can pick a roundabout design feature from the plan view to quickly edit a specific element of the roundabout.
To access the roundabout editing tool, first click the Roundabout Tools button and then the Roundabout Edit Tool button.
When the tool is active, a small white circle is drawn next to the roundabout design elements that can be modified in the plan view, as shown below:
All of these elements can also be edited from the Roundabout Junction Edit window, which also includes additional options such as entry and exit junction fillet style.
Below is a close-up of a single roundabout arm with added labels:
Each of the labelled points edits a different property. Clicking on the point will bring up a window where you can see and edit the associated property.
A: Exit fillet radius.
B: Entry fillet radius.
C: Exit lane width
D: Entry lane width
E: Exit style
The default "Parallel" style will generate a splitter island exit line that is parallel to the channelline, offset by the exit lane width. You can swap to the "Tangential" style, which will then generate in the same was as the entry side. More information on the splitter island generation can be found in the splitter island section of the roundabout junction edit help page.
F: Exit corner fillet radius.
G: Entry corner fillet radius.
H: Rear corner fillet radius.
A radius of -1m for any of these fillets will result in an automatic radius fillet being applied.
