This thesis examines the impacts of wet weather on traffic flow and signalized intersections, and it also examines the feasibility of mitigating these impacts. First a literature review was completed. Various studies showed that the impact of weather on traffic flow is a topic that is of much interest to researchers and transportation officials. Inclement weather tends to cause drivers to behave differently than they would if the weather were clear, which may cause reductions in capacity along a roadway network. It was decided to focus on rainy weather since most other studies tended to examine a variety of different weather types. Various sources of data were examined, including obtaining data from the Smart Travel Laboratory, from the Smart Travel Van, and the city of Norfolk traffic signal system. None of these sources came to fruition, due to concerns over data quality, data accuracy, safety of people and equipment, and privacy concerns. It was therefore decided to video tape an intersection in the field to obtain data on the saturation flow rates during dry and wet weather conditions. Free flow speed data was also collected during wet and dry conditions to determine if a change in desired speed existed. The saturation flow rate decreased by approximately 4.7 percent, and the free flow speeds decreased by 9.4 percent during wet weather, and both were determined to be statistically significant differences. This data was used to calibrate the VISSIM microscopic simulation model, and allow an isolated intersection to be simulated in both dry and wet conditions. When simulated under a variety of input vehicle volumes, it was determined that there are reductions in the capacity of the intersection, and increases in delay, queue lengths, travel time, and number of stops during wet weather. These increases were most noticeable when the input volumes were near the intersection’s capacity. New signal timing plans were developed to mitigate the effects of wet weather. When an optimal timing plan for dry weather was developed, improvements were noted in almost all performance measures. Additionally, the percent deterioration in performance due to wet weather was lessened by implementing an optimized timing plan. However when special wet weather timing plans were developed, no system-wide benefits were realized. The best timing plan for both wet and dry conditions appeared to be the dry-weather optimal timing plan. Therefore it is unlikely to be feasible to develop special wet weather timing plans for isolated signalized intersections. The concept of developing wet weather timing plans for arterial networks should be investigated further using field data to support results and conclusions. (Author/publisher)
Abstract