SKID RESISTANCE DATA QUALITY

The quality of the skid resistance data currently collected has been a subject of considerable debate. This situation is exacerbated by the various types of equipment involved and the variations in the methods employed when they are used. The ASTM E-274 standard has attempted to resolve the problem by specifying the equipment design and its application, but there are still modifications in the details of its application. Even when the E-274 equipment is applied identically on the same pavement section at different times, it does not provide the same results. This fact has been used to discredit the test and as one of the reasons to discontinue or not begin network testing. In reality, the variation in results is primarily the result of changes in the pavement surface condition itself. Surely the test tires are not quite identical and testing temperature plays a role, but it is the change in surface contamination that is the primary contributor to the differences experienced. Once we understand the cause of the variation and accept that the values collected represent the pavement Skid Resistance at the time of collection, we can confidently use the data to manage the Skid Resistance property of the network. The innate variability of the Skid Resistance property should certainly be taken into account in the process of discovering sections that need attention due to low Skid Resistance. Maryland’s experience with the variability of same pavement testing using E-274 locked rotor testing is that a CV of 5% can be expected when the same sections are measured over multiple summer months and several years. The highest values were measured immediately after significant summer rain storms and the lowest after long hot, dry spells. Both asphalt and concrete sections were evaluated in this study and displayed similar results.

In summary, while we are limited to an indirect test to measure pavement Skid Resistance, the data is actionable for identifying sections that need attention for low Skid Resistance.