Modeling Effects of Precipitation on Vehicle Speed: Floating Car Data Approach

Extreme precipitation as a result of the ongoing change of climatic conditions is attributed to significantly hindering vehicle circulation in urban transportation networks. During 2014, Thessaloniki, Greece, experienced significant anomalies with respect to the expected amount and intensity of rainfalls, which severely influenced traffic flow and safety conditions. According to the National Meteorological Service, a 360% deviation in the total rainfall accumulation (compared with the 1959–1997 mean) was observed in the city for July 2014. Based on the increased intensity and occurrence of such events, this research studied the impacts of heavy rainfalls on road operations, with the road network of Thessaloniki, Greece, serving as a case study. Data for these analyses were obtained from floating car data of a 1,200-taxi fleet that contained GPS coordinates and speed information. Findings reveal that vehicle speed drops increase with precipitation intensity yet they differ depending on the examined road type. This paper highlights the importance of developing a sound quantitative understanding of the effects of such events in urban areas and considers the context of the changing climate and the concomitant increasing frequency of extreme events.