Providing a safe stopping distance is an important requirement in highwayand street geometric design. A key element to this requirement is the availability of adequate tire-pavement skid resistance. This aspect has notbeen explicitly addressed in the existing practices of determining braking distance, a major component of stopping distance. In practice, the common methods of evaluating safe braking distances do not reflect the effects of factors related to tire, pavement surface and the presence of water on pavement surface. Today, equipped with a better knowledge on the mechanism of wet-weather skid resistance, a rational mechanistic interpretation ofautomobile braking distances can be made in relation to the characteristics of tire-pavement skid resistance behavior. In this paper, this is achieved using basic mechanics principles and finite-element skid resistance simulation modeling to study the implications of braking distance specifications and their relations with pavement friction management. As an illustration, this study examines the relationship between the AASHTO stopping distance requirements and the skid resistance threshold level adopted by several state pavement management authorities. In the analysis, the variation of skid resistance with vehicle speed, and the effects of wheel load, tire inflation pressure, and water-film thickness are considered. The results of the analysis highlight the need to maintain consistency between geometric design stopping distance requirements and pavement friction management to achieve safe vehicular operations.
Abstract