Results and Lessons from Local Calibration Process of the Highway Safety Manual for the State of Maryland

This paper discusses Maryland's experience in developing local calibration factors (LCFs) in the application of the Highway Safety Manual (HSM), which is the required process for adjusting predicted crashes estimated by the HSM's safety performance functions (SPFs) to local jurisdictions. The LCFs for 18 facility types were calculated with data for the period 2008 to 2010. Additional variables were gathered by alternative data collection methods. Because HSM's crash proportion was different from Maryland's, Maryland's crash proportion was used to predict crash frequency and calculate the LCFs. Maryland in general had fewer crashes than predicted crash frequency generated by the HSM's SPFs. The LCFs for 15 of 18 facility types were less than 1.0. In particular, intersection LCFs were extremely low. Because of potential issues with unreported minor and property damage only crashes, the authors recommend using the LCFs for fatal and injury crashes where available. The pairwise comparison of Maryland LCFs with the LCFs of nine case studies showed statistically significant differences between states, providing grounds for jurisdiction-specific LCF development.

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