Shunting operations at flat yards: retrieving freight railcars from storage tracks

Abstract

In this paper, we study the railcar retrieval problem (RRT) where specified numbers of certain types of railcars have to be withdrawn from the storage tracks of a flat yard. This task arises in the daily operations of workshop yards for railcar maintenance. The objective is to minimize the total cost of shunting via methods such as minimizing the usage of shunting engines.We describe the RRT formally, present a mixed-integer program formulation, and prove the general case to be NP-hard. For some special cases, exact algorithms with polynomial runtimes are proposed. We also analyze several intuitive heuristic solution approaches motivated by observed realworld planning routines. We evaluate their average performances in simulations with different scenarios and provide their worst-case performance guarantee. We show that although the analyzed heuristics result in much better solutions than the naive planning approach, they are still on average 30%-50% from the optimal objective value and may result in up to 14 times higher costs in the worst case. Therefore, we conclude that optimization should be implemented in practice in order to save valuable resources. Furthermore, we analyze the impacts of yard layout and the widespread organizational routine of presorting on the railcar retrieval cost.

Shunting Strategy for Placing-In and Taking-Out Wagons on Branch-Shaped Freight Operation Network with Simulation Method

“…Simulation methodology was adopted for evaluating and improving the PTWS in some literatures. Jaehn et al [25] evaluated performances of their heuristic solution in simulations with different scenarios and provide their worst-case performance guarantee when studying shunting operations problem at flat yards. Kieu et al [26] considered important interactions between buses and their schedules and formulated several simulation models of bus routes have been proposed in the literature, including cellularautomata, bus-following, and traffic-following models to make transit operators both better understand the dynamics of bus routes and facilitate better policymaking.…”

Rail terminal operations

“…The problem is solved exactly by an -constraint method and heuristically by a multi-directional local search procedure. Jaehn et al (2018) study the railcar retrieval problem where railcars having different types must be retrieved in certain quantities from storage tracks such that shunting costs are minimized. After presenting a MIP formulation and showing NP-hardness of the general problem, exact polynomial-time algorithms are proposed for special cases.…”

Avaliação De Capacidade De Processamento Em Pátios Ferroviários Planos De Classificação Através De Modelo De Otimização

“…O Gráfico 3.1 mostra um crescente interesse na otimização também na última década. Mesmo para os trabalhos que trazem uma abordagem heurística ou meta-heurística para resolução do problema, a modelagem matemática está presente, como acontece nos casos [8], [11], [12], [13], [14] e [15]. Com foco na modelagem matemática para otimização, em 2008, Hansmann e Zimmermann [8] se concentraram no processo de triagem que ocorre na área de mesmo nome do pátio.…”

“…[41] e Jaehn, Otto e Seifried [13] apresentaram modelos de otimização aplicados a pátios planos, porém com características de processo simplificadas frente ao tratado neste estudo. Adlbrecht et al…”

“…Esse processo, apesar de considerado independente na modelagem dos autores, complementa a classificação por hump realizada no mesmo pátio, porém em outro conjunto de linhas. O pátio plano considerado é um conjunto de linhas paralelas acessado apenas por um lado, assim como em [13], que trata da formação de um trem com vagões específicos em uma sequência arbitrária. A classificação dos vagões foi modelada em [13] através de uma programação inteira mista.…”