4. When the barriers are fully lowered their uppermost surfaces shall be not less than 900mm above the road surface at the centre of the carriageway and the under-clearance between the barriers and the road surface shall not exceed 1000mm.
4. When the barriers are fully lowered their uppermost surfaces shall be not less than 900mm above the road surface at the centre of the carriageway and the under-clearance between the barriers and the road surface shall not exceed 1000mm.