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.

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

“…), 21,814 yard accidents were extracted for this study. The processes of train type identification and classification into manifest train and unit train types, as well as yard type identification and assignment of incidents to hump and flat classification yard locations, with this dataset was detailed in a previous publication by Zhao and Dick ( 5 ). The data contains various errors and empty fields that may not be neglected.…”

“…A key difference between the yard switching methodology and that used for mainline and train A/D events is that these same derailment size probabilities (Table 7) are applied to any railcar switched in a flat yard, regardless of its position within the group of railcars being switched. This assumption is made since the probability of a yard switching derailment is calculated per railcar processed ( 5 ) and, given that railcar positions are either unknown or change during the switching process, there is no basis to adjust either the per-railcar probability of causing a derailment or the probability distribution of the number of railcars derailed based on the railcar position. However, the POD has an influence on the maximum possible number of cars derailed and when the truncated probability should be applied to account for the case where all railcars after the POD derail.…”

“…Among the three scopes of train operation involved in hazmat shipments via rail, line-haul, intermediate yards, and loading/unloading, the risk evaluation of line-haul movements along mainline routes has captured the majority of attention ( 4 ). During the period 1996–2018 (inclusive), U.S. Class 1 railroad manifest trains experienced 5514 derailments (average of 240 per year) on mainline track and 6278 (average of 273 per year) during arrival and departure (A/D) in railroad yards, while unit trains experienced 2462 mainline derailments (average of 107 per year) and 838 (average of 35 per year) derailments involving terminal operations ( 5 ). In addition, 13,300 derailments (average of 578 per year) occur in Class 1 railroad-owned classification yards during manifest train switching.…”

“…The probability of derailment in the format of derailment rates for unit trains at terminals and manifest trains at classification yards has been quantified in the previous phase of this research ( 5 ). Barkan et al ( 8 ) demonstrated that, compared with other metrics, such as monetary damage, the number of derailed railcars is a good proxy metric for the amount of energy in an accident and therefore an encouraging predictor of the conditions for a hazmat release for both risk analysis and risk management.…”

Statistical Analysis of Train Derailment Severity for Unit Trains Versus Manifest Trains

“…Current methods based on the TG model focus on limited attributes and only estimate the mean of freight train derailment severity. Limited previous research has estimated derailment severity pertaining to the use of different types of trains ( 9 , 23 , 24 ). Even fewer studies have focused on the difference between loaded and empty unit trains versus other types of trains for the same traffic demand.…”