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A parallel algorithm for train rescheduling
Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
2018 (English)In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 95, p. 545-569Article in journal (Refereed) Published
Abstract [en]

One of the crucial factors in achieving a high punctuality in railway traffic systems, is the ability to effectively reschedule the trains when disturbances occur. The railway traffic rescheduling problem is a complex task to solve both from a practical and a computational perspective. Problems of practically relevant sizes have typically a very large search space, making them time-consuming to solve even for state-of-the-art optimization solvers. Though competitive algorithmic approaches are a widespread topic of research, not much research has been done to explore the opportunities and challenges in parallelizing them. This paper presents a parallel algorithm to efficiently solve the real-time railway rescheduling problem on a multi-core parallel architecture. We devised (1) an effective way to represent the solution space as a binary tree and (2) a novel sequential heuristic algorithm based on a depth-first search (DFS) strategy that quickly traverses the tree. Based on that, we designed a parallel algorithm for a multi-core architecture, which proved to be 10.5 times faster than the sequential algorithm even when run on a single processing core. When executed on a parallel machine with 8 cores, the speed further increased by a factor of 4.68 and every disturbance scenario in the considered case study was solved within 6 s. We conclude that for the problem under consideration, though a sequential DFS approach is fast in several disturbance scenarios, it is notably slower in many other disturbance scenarios. The parallel DFS approach that combines a DFS with simultaneous breadth-wise tree exploration, while being much faster on an average, is also consistently fast across all scenarios.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 95, p. 545-569
Keywords [en]
Railway traffic; Rescheduling; Parallel depth-first search; Optimization
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:bth-16868DOI: 10.1016/j.trc.2018.07.003ISI: 000447112500032OAI: oai:DiVA.org:bth-16868DiVA, id: diva2:1239007
Projects
TRANS-FORM
Funder
Swedish Research Council Formas
Note

open access

Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-08-15
In thesis
1. Parallel algorithms for real-time railway rescheduling
Open this publication in new window or tab >>Parallel algorithms for real-time railway rescheduling
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In railway traffic systems, it is essential to achieve a high punctuality to satisfy the goals of the involved stakeholders. Thus, whenever disturbances occur, it is important to effectively reschedule trains while considering the perspectives of various stakeholders. The train rescheduling problem is a complex task to solve, both from a practical and a computational perspective. From the latter perspective, a reason for the complexity is that the rescheduling solution(s) of interest may be dispersed across a large solution space. This space needs to be navigated fast while avoiding portions leading to undesirable solutions and exploring portions leading to potentially desirable solutions. The use of parallel computing enables such a fast navigation of the search tree. Though competitive algorithmic approaches for train rescheduling are a widespread topic of research, limited research has been conducted to explore the opportunities and challenges in parallelizing them.

This thesis presents research studies on how trains can be effectively rescheduled while considering the perspectives of passengers along with that of other stakeholders. Parallel computing is employed, with the aim of advancing knowledge about parallel algorithms for solving the problem under consideration.

The presented research contributes with parallel algorithms that reschedule a train timetable during disturbances and studies the incorporation of passenger perspectives during rescheduling. Results show that the use of parallel algorithms for train rescheduling improves the speed of solution space navigation and the quality of the obtained solution(s) within the computational time limit.

This thesis consists of an introduction and overview of the work, followed by four research papers which present: (1) A literature review of studies that propose and apply computational support for train rescheduling with a passenger-oriented objective; (2) A parallel heuristic algorithm to solve the train rescheduling problem on a multi-core parallel architecture; (3) A conflict detection module for train rescheduling, which performs its computations on a graphics processing unit; and (4) A redesigned parallel algorithm that considers multiple objectives while rescheduling.

Place, publisher, year, edition, pages
Sweden: Blekinge Institute of Technology, 2019. p. 184
Series
Blekinge Institute of Technology Licentiate Dissertation Series, ISSN 1650-2140 ; 9
National Category
Computer Sciences
Identifiers
urn:nbn:se:bth-18511 (URN)978-91-7295-378-9 (ISBN)
Presentation
2019-10-17, J1640, Campus Gräsvik, Karlskrona, 09:00 (English)
Opponent
Supervisors
Available from: 2019-08-02 Created: 2019-08-02 Last updated: 2019-09-17Bibliographically approved

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Publisher's full texthttps://doi.org/10.1016/j.trc.2018.07.003

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Josyula, Sai PrashanthTörnquist Krasemann, JohannaLundberg, Lars

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