3. When the barriers are fully lowered their uppermost surfaces shall be not less than 900 mm above the road surface at the centre of the carriageway and the underclearance between the barriers and the carriageway shall not exceed 1 metre.
3. When the barriers are fully lowered their uppermost surfaces shall be not less than 900 mm above the road surface at the centre of the carriageway and the underclearance between the barriers and the carriageway shall not exceed 1 metre.