Application of Highway Crash Frequency Prediction Model for HighwayTransportation Planning

Highway safety on two-lane highways has always been a big concern for traffic engineers, since these highway facilities generally experience relatively low traffic volumes but high frequency of crashes. Annually, about one-third of the total number of highway crashes occurs on two-lane highways in Louisiana. For this reason, various improvement projects on two-lane highways have been constantly undertaken in Louisiana. Using the crash frequency prediction model to estimate the safety benefit of two-lane highways’ improvement projects provides key information to the process of highway transportation planning. This presentation will introduce the results of such a study with the historical Louisiana highway crash records and the Interactive Highway Safety Design Model (IHSDM) developed by the Federal Highway Administration (FHWA). The model estimates the expected number of highway crashes as a function of average daily traffic (ADT) and length of the segment. To apply the model, the author first calibrates the model parameters by using the actual crash frequencies on each segment from the past 11 years. The comparison between the expected number of crashes predicted by the model and the actual number of crashes are made based on which the further model stratifications are conducted. The analysis made at the disaggregated level reveals more accurate pictures on the cause of crashes. The results of this study can be used to estimate the safety impact of highway improvement projects proposed during the planning process.