For the civil cell, you would place arc elements based on offsets from the centerline so it remains ruled. I have seen some example where a point is placed for the center of the cul-de-sac and so the circulatory area rotates about the center point. Another way I have seen people create the cell is by a secondary small linear element coming off the edge of the roadway. I believe this is to create a cul-de-sac which is off-center. You may can look at some resources of other workspaces which contain civil cells on how to create one for a cul-de-sac.
