On 27 October 2015, Stuart Guthrie presented a paper to the Scottish Branch on HD 28 Investigations. HD28 is part of the Design Manual for Roads & Bridges and is primarily concerned with Skid Resistance. HD36 and Interim Advice Note 156/12 contain requirements for aggregate polished stone values.
Stuart explained that the purpose of HD28 is to describe how appropriate levels of grip on the road network will be managed. HD28 describes how measurements are made and interpreted. It is used in conjunction with HD36 which sets out advice on material characteristics and properties of surfacing materials necessary to deliver the required skid resistance properties. The term ‘skid resistance’ when referred to in the DMRB refers to the frictional properties of the road surface in wet conditions.