Surface dressings on motorway hard shoulders

Surface dressing hard shoulders of motorways with light-coloured chippings is one method of providing a contrast in colour and texture with the carriageway. The rates of spread of binder suitable for normal surface dressings on roads are unsuitable for hard shoulders which carry little or no traffic. Two full-scale experiments were made on motorway shoulders to determine the optimum rate of spread. Tar and bitumen binders were used with three-eighth of an inch and a quarter of an inch chippings, the rate of binder spread being varied. Dense tarmacadam base-course material could not be surface-dressed with three-eighth of an inch crushed-rock chippings as the necessary rate of spread of binder was too great for practical use; chippings not larger than a quarter of an inch should be used. It was deduced that gravel chippings were unsuitable for surface dressing dense coated macadam base-course material. (A)