Civil Cell Clipping

Once a civil cell is placed it's often recommended to drop the civil cell down so the design elements are no longer part of a civil cell.  Usually works out better from the Explorer, right click and drop civil cell.  Once that's done, the surface template should clip as any standard surface template.

EDIT: The civil cell has a surface template containing terrain elements (breaklines/boundaries,etc). Once your civil cell is dropped, you'll want to create that U shaped portion as boundary elements for the surface Terrain using ORD's terrain tools. You'll see this former civil-cell's terrain under Terrains in the Explorer. You may need to remove the terrain boundary element that crosses through the median.  If all works well, the segments across the lanes may not need a boundary or profiled element, unless you want to profile any minor cross slope breaks across each lane... which in that case, you'd want 2 separate elements (with active profiles) then added those two to the terrain.  Here's an video of the general concept of how that civil cell was made and the user of 2D profiled elements to build them. Old vid, but the tech has been around that long ;D 

Once a civil cell is placed it's often recommended to drop the civil cell down so the design elements are no longer part of a civil cell.  Usually works out better from the Explorer, right click and drop civil cell.  Once that's done, the surface template should clip as any standard surface template.

EDIT: The civil cell has a surface template containing terrain elements (breaklines/boundaries,etc). Once your civil cell is dropped, you'll want to create that U shaped portion as boundary elements for the surface Terrain using ORD's terrain tools. You'll see this former civil-cell's terrain under Terrains in the Explorer. You may need to remove the terrain boundary element that crosses through the median.  If all works well, the segments across the lanes may not need a boundary or profiled element, unless you want to profile any minor cross slope breaks across each lane... which in that case, you'd want 2 separate elements (with active profiles) then added those two to the terrain.  Here's an video of the general concept of how that civil cell was made and the user of 2D profiled elements to build them. Old vid, but the tech has been around that long ;D 

I tried that, but it didn't work. I dropped civil cell from Explorer, and couldn't select it after Add Corridor Clipping prompted Select Corridor to be Clipped. I don't know how civil cell was created, but the areas outside edge of pavements were selectable. The purple mesh in the image can't be selected as a corridor to be clipped.

See EDIT to my original post!