Analysis of Derailment Severity Comparing Unit Trains at Transload Terminals and Manifest Trains at Railroad Switching and Hump Classification Yards

Growing demand for the safe and efficient transportation of crude oil and other flammable liquids by rail has highlighted the need to understand the relative derailment risk of two major heavy haul freight train types operating in the U.S.A.: unit trains dedicated to a single commodity between origin and destination terminals, and manifest trains transporting carload shipments between multiple classification (marshalling) yards. Despite the low likelihood of a train derailment, understanding the factors that influence the severity of a train derailment can potentially mitigate severe consequences and improve the reliability of railway transportation. Previous studies have quantified the derailment severity of mainline transportation but excluded derailments in yards and terminals. This paper examines U.S. freight train yard and terminal derailment data between 1996 and 2018 to develop a novel event-chain-based probabilistic risk analysis specifying yard and terminal arrival and departure derailment (derailments involving trains arriving/departing a yard or terminal) severity for both manifest trains and unit trains, and yard switching derailment (derailments during railcar sorting or classification in a yard) severity for manifest trains only. The approach developed in this paper provides predictions of severity with respect to the total number railcars derailed and hazardous materials (hazmat) railcars derailed given a manifest train or unit train shipment and hazmat railcar placement within the train consist. When combined with mainline derailment risk analysis methodologies and yard derailment rates from previous research, these yard and terminal derailment severity metrics facilitate more holistic comparisons of unit and manifest train derailment risks for all components of loaded trips.