Quantitative Derailment Rate Comparison of Unit Trains at Transload Terminals and Manifest Trains at Railroad Switching and Hump Classification Yards

Abstract

The rapid expansion of demand for efficiently and safely transporting crude oil and other flammable liquids by rail in North America has highlighted the need to understand the relative derailment risk of two main freight train types operating in the United States (U.S.): unit trains and manifest trains. Previous studies have quantified the line-haul accident rates for these train types. However, the relative derailment likelihood of these two train types associated with train arrival/departure processes and yard switching operations has yet to be quantified. This study analyzes U.S. freight train traffic and yard/terminal derailment data between 1996 and 2018 by train type. For manifest trains, derailment rates are calculated per train arrival and departure in yards, and yard switching accidents per railcar handled in classification yards. For unit trains, the number of accidents per arrival and departure event in loading and unloading terminals is quantified. These rates are further refined to reflect particular unit train loading conditions and yard type for manifest trains. The analyses suggest that manifest trains have a four-times larger rate per yard arrival/departure than unit trains per terminal arrival/departure. Regardless of yard type, railcar shunting movements in classification yards are significant to the overall manifest train shipment derailment likelihood. An example case study demonstrates how a manifest train may be ten times more likely to derail than a unit train, while varying the number and type of intermediate yards for manifest train and the loading factor for unit train has distinct impacts on the overall derailment rate.