Determining the quality of highway service caused by rainfall

Previous studies on the impact of rainfall on highways have focused on quantitative appraisal and vehicle speed reduction. This study is based on the quality of highway service during rainfall. It presents a novel approach to qualitative assessment of highway service using criteria based on road provider and user perceptions. It describes a method to evaluate speed/flow curves using direct empirical data and the concept of the fundamental relationship of flow, speed and density. On-site studies for volume and speed were observed for roadways, during daylight dry weather and rainfall conditions. Results show a slight reduction in qualitative service during light and moderate rainfall, and significant reduction during heavy rainfall in all cases. The paper concludes that heavy rainfall has a significant impact on the quality of highway service and that this may lead to traffic shockwave velocity propagations.