Limitations of Using Skid Number in Accident Analysis and Pavement Management

Pavement frictional characteristics are commonly determined by conducting skid tests in accordance with ASTM Standard E274. The results of these tests [skid number (SN)] are used in ranking roads to establish construction priorities and to estimate tirepavement friction in accident analysis. The role of SN in these two applications is addressed. There are serious limitations constraining the use of SN in accident analysis as well as in pavement management. Use of SN-based estimates of coefficient of friction may lead to large errors in estimating the braking distance or initial speed of a vehicle involved in an accident. In pavement management, SN is an important factor in evaluating traffic safety; however, other factors must also be considered, such as accident history data, driving difficulty, road geometry, and traffic characteristics. A wet pavement index, incorporating all factors relevant for traffic safety under wet weather conditions, should be developed to provide a basis for pavement management decisions related to highway safety.