Calibration of the Highway Safety Manual Predictive Models for Rural Two-Lane Roads for Vermont

The 2010 Highway Safety Manual (HSM) developed by AASHTO provides predictive equations for quantifying the safety effects of planning and designing roadway alternatives. These equations have been, however, developed based on data sets from a small number of states and they must be calibrated to local conditions in order to ensure that the results at the local levels are accurate. Once the Vermont Agency of Transportation (VTrans) has a calibrated set of equations, VTrans will be able to predict crashes more accurately and be able to better evaluate project alternatives. HSM equations are a great tool to quantify safety, but because they are not calibrated for Vermont, VTrans has not been able to fully benefit from their use. Calibration factors will be developed for roadway segments and for intersections. Specifically, calibration factors will be computed for undivided-two lane, two-way roadway segments, unsignalized three-leg intersections (stop control on minor approach), unsignalized four-leg intersections (stop control on both minor road approaches) and signalized four-leg intersection. In addition, the default values in the Part C Predictive Models will be replaced with values specific to Vermont conditions.