Citation

Rajabi M, Ogle JH, Gerard P. Transp. Res. Rec. 2018; 2672(30): 99-108.

Affiliation

Civil Engineering, Clemson University, Clemson, SC 2Applied Statistics, Clemson University, Clemson, SC Corresponding Author: Address correspondence to Mahdi Rajabi: mrajabi@clemson.edu

Copyright

(Copyright © 2018, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

10.1177/0361198118788205

PMID

unavailable

Abstract

The publication of the Highway Safety Manual (HSM) in 2010 established crash frequency prediction as the essential safety measure for safety studies. However, given that the models were developed using a single state's data, the HSM recommends calibration of the prediction models using data from the jurisdiction where they will be applied. This calibration process has been conducted in several states and many questions have been raised as a result. This paper is intended to investigate different definitions and criteria for the calibration factors, and provide recommendations for practitioners on which definition to use. In addition to the calibration factors in the HSM and previously published definitions, two other calibration factor equations are proposed and compared using multiple goodness of fit measures. Whereas each definition may outperform others in certain measures, in this study, it is recommended to use the definition that maximizes the likelihood between predicted and observed crashes. The idea is to follow the same concept in both state-specific safety performance functions development and calibration process, which is maximizing the likelihood of predicted and observed crashes.

Language: en