This report documents the development of two wet weather safety indices. One, WWSI sub a, is an analytical index developed from a number of preceding analytical and empirical studies of tire-pavement friction, vehicle handling and stability, and potential for hydroplaning and visibility during periods of rainfall which is a site-specific formulation providing highway engineers with a capability of selecting appropriate combinations of road surface geometrics, surface textures and skid numbers for the design of road elements as well as a way to analyze existing sites. The other, WWSI sub e, is an empirical formation based on prediction equations for wet accident rates which were derived by multiple regression techniques from a survey of sixty highway segments in Texas covering a range of wet accident rates from zero to 40 accidents per year per mile. In general, much higher values for wet accident rates and sensitivity to pavement skid resistance is much higher in urban than in rural areas
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