Developing Calibration Factors for Crash Prediction Models with Consideration of Crash Recording Threshold Change

The focus of this paper is on presenting a revised method to develop calibration factors (CFs) with consideration of the change in the crash recording threshold (CRT), which is a minimum value to report crashes. The higher the CRT, the fewer the number of recorded property damage only (PDO) crashes. In this paper, a threshold adjustment factor was defined and used to estimate the new CFs. Because the threshold change affects only the total number of crashes and the PDO crashes, the percentage of fatal and injury (F/I) crashes before the threshold change needs to be adjusted to properly estimate the total number of F/I crashes. The revised method was verified with case studies using Illinois data. Five years of crash data were gathered and used to develop CFs for five roadway types, including two-lane undivided (2U), two-lane with a two-way left-turn lane (3T), four-lane undivided (4U), four-lane divided (4D), and four-lane with a two-way left-turn lane (5T). Because of an increase in the CRT in 2009, a method is needed to supplement the standard approach to adjust CFs with consideration of the effect of the new CRT. The CFs for 2U and 3T before–after considering the threshold adjustment factor were 1.44/1.32 and 1.24/1.12, respectively, while the CFs before–after the threshold change for 4U, 4D, and 5T were 0.99/0.85, 0.68/0.55, and 0.77/0.69, respectively. The results proved that the revised method can help state and local agencies predict the number of crashes without redeveloping new CFs resulting from the change in CRT.