The Safety Performance Function (SPF) is a predictive tool used by practitioners to predict the crash frequency given a set of road and traffic conditions in the future. However, the development of SPFs is based on the archived data, through estimating Negative Binomial (NB) models to capture the relationships between the crash frequency and contributing variables in the past. A misconnection may exist between the development and application of SPFs if the temporal variations in the relationships between safety performance and factors are not fully captured in SPF development negative binomial. This study proposes a methodology to develop SPFs that can represent the future relationships between factors in safety performance. Such SPFs are called “Future Safety Performance Functions” or “F-SPFs”. This method has two main steps: 1) the temporally weighted NB modeling is employed to estimate a local SPF for each historical timestamp, and 2) a series of time-series models are estimated to identify the trend of the temporal variations of local SPFs and project an F-SPF for a future timestamp. A case study is performed for the rural divided multilane highways in Georgia to demonstrate the development of F-SPFs. The crash dataset provides adequate temporal variations from 2013-2019. This study will offer valuable insights to both researchers and practitioners in the transportation safety area regarding the temporal variations or uncertainties in relationships between safety performance and contributing factors. The methodology proposed in this research is expected to advance the practice of using SPFs by providing improved information for the decision-making of transportation safety improvement projects.     

Developing Future Safety Performance Functions (F-SPFs): A Temporal Approach Integrated with Time-Series Modeling

ASCE International Conference on Transportation & Development (ICTD 2021) is organized by the Transportation & Development Institute (T&DI) of ASCE to facilitate the exchange of information, knowledge, and best practices among transportation and development practitioners and researchers, public infrastructure owners, policymakers, government engineers and planners, operations managers, and leading academics from around the world.

Paper Proceedings: https://doi.org/10.1061/9780784483534 | https://doi.org/10.1061/9780784483541

Conference DOI: https://doi.org/10.26226/m.631784867747920012e73503