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Program Prioritization And Evaluation B - 3 P' 2e t 1%e t e B.2.4 Final Crash Prediction Equation The following formula was developed for use in prioritizing highway railroad grade crossing safety improvements using Part 924, Title 23, United States Code. t = -9.21 + 1.14Log10 (A(T + 0.5)) + 0.014V + 0.008S - 0.63L And, Where, t = A temporary value used to simplify the mathematical expression. A = Vehicles per day or Average Daily Traffic (ADT). T = Average number of trains per day. V = Posted vehicle speed limit (MPH). Note - geometry may dictate a lower speed. S = Maximum train speed (MPH). = 2.71828182845904523536... (constant) L = For, Topic No. 725-080-002 March 2000 Rail Manual P )'P H PY Crossing with active warning devices use L = 1. Crossing with passive devices or no warning devices use L = 0. P = Predicted Number Of Crashes Per Year. The Predicted Number Of Crashes Per Year (P) is adjusted for crash history. Although this introduces a mathematical bias, it is needed to ensure that all possible hazardous situations are investigated. The Crash Prediction Model explains less than half of the crash environment, whereas human failure is almost always involved. Locations experiencing non predicted crashes should receive special investigation. The phenomenon of regression toward the mean may apply because a crossing that has two (2) to three (3) crashes one year may not have any more until it reaches its Actual Predicted Crash Rate. The Crash History Adjustment Equation always increases (never decreases) the crash predictor. The following adjustment for crash history is only calculated when the crash history is greater than the crash prediction. Where, P' = Crash prediction adjusted for crash history. P = Predicted number of crashes per year. H = Number of crashes for the six (6) year history or since the last warning device upgrade. Y = Number of years of crash history.
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