| This research developed a methodology to estimate rain-related data which reflect real-time weather conditions during rainfall. This methodology was applied to model highway crash frequency and severity, as well as weather-sensitive traffic parameter adjustments in traffic simulation. In this research, three primary tasks were performed to examine the impact of rain on highway safety.;The first task involved data estimation, particularly water film depth and visibility under rainfall based on existing Wisconsin crash, traffic, road geometry and weather data. The second task was statistical modeling of Wisconsin highway safety with the estimated rain-related data. Poisson or negative binomial regression models were considered to predict crash frequency, and forward and backward sequential logistic regression models were compared to predict crash severity. The final task was to simulate wet road surface traffic under weather-sensitive parameter adjustments through VISSIM. Combining adjustments of vehicle deceleration rate, traffic speed and headway time, five scenarios were constructed for the rainy weather traffic simulation.;As a result of highway safety modeling, negative binomial regression, forward and backward sequential logistic regression models were found to be optimal to estimate crash frequency, single- and multi-vehicle crash severities, respectively. Rainfall intensity and water film depth were clearly identified as significant factors to estimate rainy weather highway safety as well as speed limit and road geometry factors. In traffic simulation results, traffic operations on wet road surfaces were most effectively modeled under the adjustments in both desired speed distribution and vehicle deceleration rate function.;Through the results of this research, the impacts of rain-related factors on disaggregate level of highway safety were clearly and microscopically quantified by a novel methodology of weather data estimation. Furthermore, weather-sensitive parameters were uniquely adjusted for rainy weather traffic simulation applying the methodology of weather data estimation. Consequently, weather effects on traffic operations were modeled by traffic simulation, which will be expanded to evaluate safety decision in adverse weather conditions. |
