ABSTRACT：Safety performance functions (SPFs) or crash prediction models have played an important role in identifying the contributing factors of crashes, predicting crash counts, identifying hotspots, etc. Because it needs a lot of time and efforts to estimate a SPF, previous studies have evaluated if a SPF could be applied to data from other regions, i.e., transferability. Although many efforts have been made for micro-level SPF transferability, not many have been done for macro-level SPF transferability. Transferability analysis of macro-level SPFs in the international context, especially between western countries, has not been conducted. Therefore, the authors evaluate the transferability of SPFs of several states in the United States (i.e., Illinois, Florida, and Colorado) and Italy in this study. The SPFs were developed using data from counties in the United States and provincias in Italy, and the results show that there are multiple common significant variables across the countries. Subsequently, transfer indexes are calculated between the developed SPFs, and the indexes show that the Italian SPFs for total and bicyclists crashes are transferable to U.S. data after calibration factors are applied while the U.S. total and bicycle SPFs, except for the Colorado SPF, cannot be transferred to the Italian data. On the other hand, none of the developed pedestrian SPFs are transferable to other countries. This paper provides insights into the applicability of macro-level SPFs between the U.S. and Italy, and shows a good potential of international SPFs’ transferability. Nevertheless, further investigation is needed for the SPF transferability between more countries.
Jaeyoung Lee, Mohamed Abdel-Aty, Maria Rosaria De Blasiis, Xuesong Wang, Ilaria Mattei. International Transferability of Macro-Level Safety Performance Functions: A Case Study of the United States and Italy. Transportation Research Board 98th Annual Meeting, Washington D.C., USA, 2019. 1.12-17.