Function map_model::make::initial::geometry::on_off_ramp

fn on_off_ramp(
    roads: &mut BTreeMap<OriginalRoad, Road>, 
    i: NodeID, 
    lines: Vec<(OriginalRoad, Pt2D, PolyLine, PolyLine)>
) -> Option<(Polygon, Vec<(String, Polygon)>)>