Results and lessons from local calibration process of the Highway Safety Manual for the state of Maryland: Freeway segments, speed-change lanes, and ramp terminals

Abstract

In 2014, the authors successfully developed local calibration factors (LCFs) for the rural and urban arterials and highways for the State of Maryland. In this research, the authors computed LCFs for freeway segments, speed-change lanes, and signalized and stop-controlled ramp terminals to complement and complete LCFs for Maryland to adjust predicted motor vehicle crashes as part of the Highway Safety Manual (HSM) application. Implementing the HSM requires local calibration or development of jurisdiction-specific models. Either one is a laborious and challenging process because, despite being explained in the manual, the process is not easy or straightforward. Thus, the main contribution of this article is providing a detailed case study of the most complete calibration effort with the HSM Supplement models. Furthermore, the current state of the HSM Supplement adoption by different states is discussed. The results of the conducted research are summarized including the LCF development procedure and challenges that the authors had to overcome as well as some suggestions. LCFs were computed for data from a three-year study period (2008–2010) from multiple resources of Maryland government agencies. Ramps and collector-distributor (C-D) roads were excluded due to insufficient historical crash data. Baltimore City was also excluded because of a different data collection scheme.