Caltrans sought assistance to lay out a plan for calibrating the Highway Safety Manual’s (HSM) safety performance functions. The calibration allows Safety Performance Functions (SPF) developed with data from one jurisdiction to be applied more accurately in a new jurisdiction.
Kittelson helped Caltrans with a Calibration Framework Plan to develop a prioritized approach for calibrating the HSM and 2014 HSM Update safety performance functions for California. Kittelson evaluated the available Caltrans data and requirements for the HSM SPFs to understand the ability to calibrate each SPF and data collection needs for each SPF. The calibration framework also outlines the practical application of each HSM SPF processes to prioritize calibration of SPFs that are most likely to be used widely by Caltrans staff, local agencies, and consultants in evaluating the safety performance of project alternatives. The final step of the calibration framework will recommend an action plan for Caltrans to implement calibration and recommend context-specific calibration needs to account for the state’s diverse geography and driver behavior.
Based on the Calibration Framework Plan, a subset of Safety Performance Functions (SPFs) were identified as feasible for calibration. The plan includes additional supporting materials for Caltrans to make the case on the value of calibration to their executive team moving forward.