Development and use of a skidding strategy for a local authority

At the previous Cheltenham Conference in 2008 the first author presented a paper [Catt 2008] describing the development of a local authority skidding strategy. This paper presents the developments, refinements and use of that strategy. In essence it is a local authority version of the Highways Agency's HD28. It describes why the original investigation levels (IL) were set at those recommended by the Highways Agency for use on trunk roads and motorways. As part of the strategy it was decided to simplify the characteristic SCRIM coefficient (CSC) by using the average of the last three years data. The paper describes the process by which site investigations are carried out, the collection of data, the use of that data including CSC (of course) together with injury collision data for the same 3 year period, SCANNER data including texture, rut depth and ride quality. The paper discusses the reasons for their use. Additionally the paper describes various information obtained during the use of the strategy including a general reduction of IL in 30 mph areas, additional classes in the IL table, anomalous relationships between PSV and CSC, and comparison of collision risk at pedestrian crossing with and without high friction surfacing. All of the above have now been incorporated in the revised strategy published in 2013. This is described in the paper. Further refinement of the strategy will occur as more knowledge is gained of the inter-relationship between surface characteristics and crashes.