Edit road geometry
- Open or create simple road line
- Add center line
- Add one line on both side of it

- Then add ditch slopes for the side lines
- Click Tools --> Copy line
- Select Position, Method, Offset and slope and you will see a preview (green line) of the new line

- Press Apply to create new line
- Select the previous line and add another line like in the picture

- Press Apply to create new line
- Select the previous line and add another line like in the picture

- Press Apply to create new line
- Then repeat the same steps on the other side of the original road (select Position:Inside for these)
- After that the road should look like this
- Save/Export it in the format you like

- Perform triangulation Sidebar --> Edit surface model --> Edit surface

- Then you should have a nice triangulated road with ditches on both sides
- Use Tools --> Cross Section to check the file

- Save/Export it in the format you like