LOSS Evaluation for Continuous Downgrades Segments Based on Accident Frequency Prediction

Abstract

In order to evaluate traffic safety performance of continuous downgrades segment more accurately and quantitatively, a new safety evaluation method namely level of safety service (LOSS) is introduced. Based on the current traffic safety situation in China, the LOSS definition and classification method are studied systematically. In this paper, LOSS is built as a 5 levels framework and the graded threshold values are derived from accident frequency prediction models. The empirical research dataset includes 322 accidents data on a 15.27km continuous downgrades segment. The dataset is grouped into 16 fixed longitudinal grade sections to highlight the geometrical characteristics. Negative binomial model is best fitted among four candidate models, while the parameter estimation result indicates that geometrical factors, oversize vehicles mixed rate and average speed have significant positive effect on accident frequency. The overall LOSS of sample segment locates into the Level 3 interval, which means less safety performance than expected. As an extended application, LOSS specific to each fixed longitudinal grade section is analyzed.