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  • 1. Andersson, Emma
    et al.
    Peterson, Anders
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, School of Computing.
    Quantifying railway timetable robustness in critical points2013In: Journal of Rail Transport Planning and Management, ISSN 2210-9706, Vol. 3, no 3, p. 95-110Article in journal (Refereed)
    Abstract [en]

    Several European railway traffic networks experience high capacity consumption during large parts of the day resulting in delay-sensitive traffic system with insufficient robustness. One fundamental challenge is therefore to assess the robustness and find strategies to decrease the sensitivity to disruptions. Accurate robustness measures are needed to determine if a timetable is sufficiently robust and suggest where improvements should be made.Existing robustness measures are useful when comparing different timetables with respect to robustness. They are, however, not as useful for suggesting precisely where and how robustness should be increased. In this paper, we propose a new robustness measure that incorporates the concept of critical points. This concept can be used in the practical timetabling process to find weaknesses in a timetable and to provide suggestions for improvements. In order to quantitatively assess how crucial a critical point may be, we have defined the measure robustness in critical points (RCP). In this paper, we present results from an experimental study where a benchmark of several measures as well as RCP has been done. The results demonstrate the relevance of the concept of critical points and RCP, and how it contributes to the set of already defined robustness measures

  • 2. Davidsson, Paul
    et al.
    Henesey, Lawrence
    Ramstedt, Linda
    Törnquist, Johanna
    Wernstedt, Fredrik
    Agent-Based Approaches to Transport Logistics2004Conference paper (Refereed)
    Abstract [en]

    This paper provides a survey of existing research on agent-based approaches to transportation and traffic management. A framework for describing and assessing this work will be presented and systematically applied. We are mainly adopting a logistical perspective, thus focusing on freight transportation. However, when relevant, work of traffic and transport of people will be considered. A general conclusion from our study is that agent-based approaches seem very suitable for this domain, but that this still needs be verified by more deployed system.

  • 3. Davidsson, Paul
    et al.
    Henesey, Lawrence
    Ramstedt, Linda
    Törnquist, Johanna
    Wernstedt, Fredrik
    An Analysis of Agent-Based Approaches to Transport Logistics2005In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X , Vol. 13, no 4, p. 255-271Article in journal (Refereed)
    Abstract [en]

    This paper provides a survey of existing research on agent-based approaches to transportation and traffic management. A framework for describing and assessing this work will be presented and systematically applied. We are mainly adopting a logistical perspective, thus focusing on freight transportation. However, when relevant, work of traffic and transport of people will be considered. A general conclusion from our study is that agent-based approaches seem very suitable for this domain, but that this still needs to be verified by more deployed system.

  • 4. Davidsson, Paul
    et al.
    Ramstedt, Linda
    Törnquist, Johanna
    Inter-Organization Interoperability in Transport Chains Using Adapters Based on Open Source Freeware2005Conference paper (Refereed)
    Abstract [en]

    The significance of electronic information exchange in transport chains and its influence on the performance of the logistics processes is well known. While much focus is still on the various techniques for information exchange, many SMEs experience problems that are not primarily caused by an absence of technology. Several advanced solutions exist but investment possibilities within many SMEs are very limited while their needs for electronic data exchange may be very similar as for the large companies. We describe a general “adapter” solution based on open source freeware that make it possible (in principle) for any business system to exchange information with any other business system. It has been successfully applied in a pilot study involving two companies (the transport operator being an SME) using different business systems (Hogia Mobilast and Movex). The solution was evaluated with the result that it met the requirements of the companies and is now planned to be used for future data exchange between the companies.

  • 5.
    Gholami, Omid
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    A Heuristic Approach to Solving the Train Traffic Re-Scheduling Problem in Real Time2018In: Algorithms, ISSN 1999-4893, E-ISSN 1999-4893, ISSN 1999-4893, Vol. 11, no 4, p. 1-18, article id 55Article in journal (Refereed)
    Abstract [en]

    Effectiveness in managing disturbances and disruptions in railway traffic networks, when they inevitably do occur, is a significant challenge, both from a practical and theoretical perspective. In this paper, we propose a heuristic approach for solving the real-time train traffic re-scheduling problem. This problem is here interpreted as a blocking job-shop scheduling problem, and a hybrid of the mixed graph and alternative graph is used for modelling the infrastructure and traffic dynamics on a mesoscopic level. A heuristic algorithm is developed and applied to resolve the conflicts by re-timing, re-ordering, and locally re-routing the trains. A part of the Southern Swedish railway network from Karlskrona centre to Malmö city is considered for an experimental performance assessment of the approach. The network consists of 290 block sections, and for a one-hour time horizon with around 80 active trains, the algorithm generates a solution in less than ten seconds. A benchmark with the corresponding mixed-integer program formulation, solved by commercial state-of-the-art solver Gurobi, is also conducted to assess the optimality of the generated solutions.

  • 6. Gustafsson, Inger
    et al.
    Törnquist, Johanna
    Customer oriented rail traffic management: a pragmatic approach to facilitate competition on the tracks.2002Conference paper (Refereed)
  • 7. Henesey, Lawrence
    et al.
    Törnquist, Johanna
    Enemy at the gates: Introduction of Multi-Agents in a Terminal Information Community.2002Conference paper (Refereed)
    Abstract [en]

    The multi-agent system (MAS) approach which offers suitable means of control, coordination and management in container terminal domain is discussed. The transport providers and actors can improve individual performance and service by sharing information with introduction of 'information society' to logistics chains. The actors involved in physical and information flows are mapped with agents who have abilities to search, coordinate, communicate and negotiate with other agents in order to complete the specified gaol in MAS approach. The information society members benefits from information sharing with use of multi-agents.

  • 8.
    Iqbal, Syed Muhammad Zeeshan
    et al.
    Blekinge Institute of Technology, School of Computing.
    Grahn, Håkan
    Blekinge Institute of Technology, School of Computing.
    Törnquist Krasemann,, Johanna
    Blekinge Institute of Technology, School of Computing.
    A parallel heuristic for fast train dispatching during railway traffic disturbances: Early results2012Conference paper (Refereed)
    Abstract [en]

    Railways are an important part of the infrastructure in most countries. As the railway networks become more and more saturated, even small traffic disturbances can propagate and have severe consequences. Therefore, efficient re-scheduling support for the traffic managers is needed. In this paper, the train real-time re-scheduling problem is studied in order to minimize the total delay, subject to a set of safety and operational constraints. We propose a parallel greedy algorithm based on a depth-first branch-and-bound search strategy. A number of comprehensive numerical experiments are conducted to compare the parallel implementation to the sequential implementation of the same algorithm in terms of the quality of the solution and the number of nodes evaluated. The comparison is based on 20 disturbance scenarios from three different types of disturbances. Our results show that the parallel algorithm; (i) efficiently covers a larger portion of the search space by exchanging information about improvements, and (ii) finds better solutions for more complicated disturbances such as infrastructure problems. Our results show that the parallel implementation significantly improves the solution for 5 out of 20 disturbance scenarios, as compared to the sequential algorithm.

  • 9.
    Iqbal, Syed Muhammad Zeeshan
    et al.
    Blekinge Institute of Technology, School of Computing.
    Grahn, Håkan
    Blekinge Institute of Technology, School of Computing.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, School of Computing.
    Multi-Strategy Based Train Re-Scheduling During Railway Traffic Disturbances2013Conference paper (Refereed)
    Abstract [en]

    Disruptions and delays in railway traffic networks due to different types of disturbances is a frequent problem in many countries. When disruptions occur, the train traffic dispatchers may need to re-schedule the traffic and this is often a very demanding and complicated task. To support the train traffic dispatchers, we propose to use a parallelized multi-strategy based greedy algorithm. This paper presents three different parallelization approaches: (i) Single Strategy with a Partitioned List (i.e. the parallel processes originate from different starting points), (ii) Multiple Strategies with a Non-Partitioned List, and (iii) Multiple Strategies with a Partitioned List. We present an evaluation for a busy part of the Swedish railway network based on performance metrics such as the sum of all train delays at their final destinations and the number of delayed trains. The results show that parallelization helps to improve the solution quality. The parallel approach (iii) that combines all re-scheduling strategies with a partitioned list performs best among the three parallel approaches when minimizing the total final delay. The main conclusion is that the multi-strategy based parallel approach significantly improves the solution for 11 out of 20 disturbance scenarios, as compared to the sequential re-scheduling algorithm. The approach also provides an increased stability since it always delivers a feasible solution in short time.

  • 10.
    Josyula, Sai Prashanth
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Passenger-oriented Railway Traffic Re-scheduling: A Review of Alternative Strategies utilizing Passenger Flow Data2017Conference paper (Refereed)
    Abstract [en]

    Developing and operating seamless, attractive and efficient public transport services in a liberalized market requires significant coordination between involved actors, which is both an organizational and technical challenge. During a journey, passengers often transfer between different transport services. A delay of one train or a bus service can potentially cause the passenger to miss the transfer to the subsequent service. If those services are provided by different operators and those are not coordinated and the information about the services are scattered, the passengers will suffer. In order to incorporate the passenger perspective in the re-scheduling of railway traffic and associated public transport services, the passenger flow needs to be assessed and quantified. We therefore perform a survey of previous research studies that propose and apply computational re-scheduling support for railway traffic disturbance management with a passenger-oriented objective. The analysis shows that there are many different ways to represent and quantify the effects of delays on passengers, i.e.“passenger inconvenience”. In the majority of the studies, re-scheduling approaches rely on historic data on aggregated passenger flows, which are independent of how the public transport services are re-scheduled. Few studies incorporate a dynamic passenger flow model that reacts based on how the transport services are re-scheduled. None of the reviewed studies use real-time passenger flow data in the decision-making process. Good estimations of the passenger flows based on historic data are argued to be sufficient since access to large amounts of passenger flow data and accurate prediction models is available today.

  • 11.
    Josyula, Sai Prashanth
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Lundberg, Lars
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    A parallel algorithm for multi-objective train reschedulingManuscript (preprint) (Other academic)
  • 12.
    Josyula, Sai Prashanth
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Lundberg, Lars
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    A parallel algorithm for train rescheduling2018In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 95, p. 545-569Article in journal (Refereed)
    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.

  • 13.
    Josyula, Sai Prashanth
    et al.
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Lundberg, Lars
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science.
    Exploring the Potential of GPU Computing in Train Rescheduling2019In: Proceedings of the 8th International Conference on Railway Operations Modelling and Analysis, Norrköping, 2019., 2019Conference paper (Refereed)
  • 14.
    Khoshniyat, Fahimeh
    et al.
    Linköpings universitet, SWE.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Analysis of strengths & weaknesses of a MILP model for revising railway traffic timetables2017In: OpenAccess Series in Informatics, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2017, Vol. 59, article id 131022Conference paper (Refereed)
    Abstract [en]

    A railway timetable is typically planned one year in advance, but may be revised several times prior to the time of operation in order to accommodate on-demand slot requests for inserting additional trains and network maintenance. Revising timetables is a computationally demanding task, given the many dependencies and details to consider. In this paper, we focus on the potential of using optimization-based scheduling approach for revising train timetables during short term planning, from one week to few hours before the actual operation. The approach relies on a MILP (Mixed Integer Linear Program) model which is solved by using the commercial solver Gurobi. In a previous experimental study, the MILP approach was used to revise a significant part of the annual timetable for a sub-network in Southern Sweden to insert additional trains and allocate time slots for urgent maintenance. The results showed that the proposed MILP approach in many cases generates feasible, good solutions rather fast. However, proving optimality was in several cases time-consuming, especially for larger problems. Thus, there is a need to investigate and develop strategies to improve the computational performance. In this paper, we present results from a study, where a number of valid inequalities has been selected and applied to the MILP model with the aim to reduce the computation time. The experimental evaluation of the selected valid inequalities showed that although they can provide a slight improvement with respect to computation time, they are also weakening the LP relaxation of the model.

  • 15.
    Krasemann, Johanna Törnquist
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Design of an effective algorithm for fast response to the re-scheduling of railway traffic during disturbances2012In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 20, no 1, p. 62-78Article in journal (Refereed)
    Abstract [en]

    An attractive and sustainable railway traffic system is characterized by having a high security, high accessibility, high energy performance and offering reliable services with sufficient punctuality. At the same time, the network is to be utilized to a large extent in a cost-effective way. This requires a continuous balance between maintaining a high utilization and sufficiently high robustness to minimize the sensitivity to disturbances. The occurrence of some disturbances can be prevented to some extent but the occurrence of unpredictable events are unavoidable and their consequences then need to be analyzed, minimized and communicated to the affected users. Valuable information necessary to perform a complete consequence analysis of a disturbance and the re-scheduling is however not always available for the traffic managers. With current conditions, it is also not always possible for the traffic managers to take this information into account since he or she needs to act fast without any decision-support assisting in computing an effective re-scheduling solution. In previous research we have designed an optimization-based approach for re-scheduling which seems promising. However, for certain scenarios it is difficult to find good solutions within seconds. Therefore, we have developed a greedy algorithm which effectively delivers good solutions within the permitted time as a complement to the previous approach. To quickly retrieve a feasible solution the algorithm performs a depth-first search using an evaluation function to prioritise when conflicts arise and then branches according to a set of criteria.

  • 16.
    Lamorgese, Leonardo
    et al.
    Optrail, ITA.
    Mannino, Carlo
    Universitetet i Oslo, NOR.
    Pacciarelli, Dario
    Universita degli Studi Roma Tre, ITA.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Train Dispatching2018In: Handbook of Optimization in the Railway Industry / [ed] Borndörfer, R. (et al.), Springer New York LLC , 2018, 268, p. 265-283Chapter in book (Refereed)
    Abstract [en]

    Train rescheduling problems have received significant attention in the operations research community during the past 20–30 years. These are complex problems with many aspects and constraints to consider. This chapter defines the problem and summarizes the variety of model types and solution approaches developed over the years, in order to address and solve the train dispatching problem from the infrastructure manager perspective. Despite all the research efforts, it is, however, only very recently that the railway industry has made significant attempts to explore the large potential in using optimization-based decision-support to facilitate railway traffic disturbance management. This chapter reviews state-of-practice and provides a discussion about the observed slow progress in the application of optimization-based methods in practice. A few successful implementations have been identified, but their performance as well as the lessons learned from the development and implementation of those system are unfortunately only partly available to the research community, or potential industry users. © 2018, Springer International Publishing AG.

  • 17.
    Ramstedt, Linda
    et al.
    Sweco AB, SWE.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Davidsson, Paul
    Malmö Högskola, SWE.
    Movement of people and goods2013In: Understanding Complex Systems / [ed] Edmonds B., Meyer R. (eds), Springer Verlag , 2013, no 9783319669472, p. 705-720Chapter in book (Refereed)
    Abstract [en]

    Due to the continuous growth of traffic and transportation and thus an increased urgency to analyze resource usage and system behavior, the use of computer simulation within this area has become more frequent and acceptable. This chapter presents an overview of modeling and simulation of traffic and transport systems and focuses in particular on the imitation of social behavior and individual decision-making in these systems. We distinguish between transport and traffic. Transport is an activity where goods or people are moved between points A and B, while traffic is referred to as the collection of several transports in a common network such as a road network. We investigate to what extent and how the social characteristics of the users of these different traffic and transport systems are reflected in the simulation models and software. Moreover, we highlight some trends and current issues within this field and provide further reading advice. © 2017, Springer International Publishing AG.

  • 18. Törnquist, Johanna
    Computer-based decision support for handling uncertainty in railway traffic and transportation2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Railway transportation has great potential, but interdependencies in the railway traffic make trains very sensitive to disturbances, which can bedifficult to handle. Using railway in an intermodal transport chain may complicate the interconnections with other modes if there is large uncertainty in the performance of the railway. A study based on interviews with several customers of the Swedish National Railway Administration shows that the customers lack information regarding occurrences of disturbances and the consequences for their trains, i.e. the new estimated time of arrival. This information is necessary when taking actions within the customers’ organisation to minimise the negative impacts. Predicting the consequences of a disturbance and the effects of counter measures taken by the Swedish train traffic managers is today an overwhelming task considering there is no computational decision support available. However, provided that the traffic and decision-making could be simulated, the effects from disturbances and actions taken could be computed. Requirements regarding computational time for a simulation are obviously significant and affect the usefulness in a real-time environment. For strategic purposes, a simulator could also serve as an analytical tool for evaluating strategies for handling certain types of disturbances. An approach to model the different layers of such a simulator, taken into account the infrastructure, the traffic flow and the influence of the traffic management decisions and transport operators, is presented. The part that covers the interaction between train traffic and infrastructure has been implemented as a small-scale discrete-event simulator. The simulator is extended by an optimisation approach, attempting to act as decision support for the train traffic managers when handling disturbances by generating effective counter measures. It is composed by a linear model specifying the timetable of a sub-network and solved by optimisation software. Iteratively, a heuristic is applied to modify the timetable by changing meets and overtakes and generate a new updated linear model to be solved. In addition to consider the train traffic system as an explicit part of a transport chain, it can be seen as a black box where some relations between input and output are known. We have investigated how uncertainty in the reliability related to one or several transport links can be handled when combining several links into a transport chain. A simulation-based approach is proposed.

  • 19. Törnquist, Johanna
    Computer-based decision support for railway traffic scheduling and dispatching: A review of models and algorithms2006Conference paper (Refereed)
  • 20. Törnquist, Johanna
    Conflict resolution policies and objectives in railway traffic disturbance management: An experimental study2007Conference paper (Refereed)
  • 21. Törnquist, Johanna
    Dynamic railway traffic management during disturbances: focus on the complexity imposed by deregulation2008Conference paper (Refereed)
    Abstract [en]

    While the railway traffic volumes in Europe continuously are increasing, the networks are facing difficulties to meet the demand and suffer from congestion and disturbances that cause insufficient reliability. The need to forecast the effects of the disturbances and efficiently re-schedule the traffic becomes evident, and especially in a deregulated network, where several private operators with competing objectives share the same tracks. This paper presents results from an experimental study where five re-scheduling policies were evaluated by simulation using real data: Three optimisation-based policies that minimise the total final delay, the accumulated delay and the delay costs respectively, one First- Come-First-Served policy, and one policy prioritising trains on time. The optimisationbased policies performed overall best, but required more computation time.

  • 22. Törnquist, Johanna
    Railway traffic disturbance management2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    With the increasing traffic volumes in many railway networks and reports on capacity deficiencies that result in insufficient punctuality and reliability, the need for efficient disturbance management solutions becomes evident. This thesis focuses on solutions that aim to minimise the consequences of disturbances for the various stakeholders and specifically on methods for re-scheduling the traffic. Railway traffic re-scheduling is a complex task with many influencing factors to consider and multiple stakeholders with sometimes conflicting interests. This problem is typically handled manually by traffic dispatchers that have a very limited access to support systems to facilitate their decision-making. This limitation hampers the possibilities to achieve sustainable and system-optimal decision-making and to provide the stakeholders with reliable traffic prognoses. We first study how railway traffic system users experience and are affected by the way the disturbances are communicated and handled by the traffic dispatchers. The results indicate that the disturbance-related information provided by the dispatchers is currently insufficient. The stakeholders need to acquire improved prognoses of their traffic and immediate part of the network to internally be able to minimise the negative effects of the disturbances. Furthermore, an analysis of the disturbance management problem structure and how the problem can be modelled is provided. The analysis shows that there exist fundamental restrictions in the traffic system that bounds the traffic flow but also a large number of context-dependent considerations such as sustaining certain connections or prioritising specific trains. The prevalence and feasibility of such considerations are difficult to identify and model. Moreover, the objectives of the disturbance management are vague and partly unclear, and therefore it is also difficult to measure and evaluate the outcome of the corresponding decision-making. Finally, a number of optimisation-based solution approaches with the purpose to facilitate for the dispatchers and their decision-making has been developed. The performance and applicability of the approaches have been evaluated for various disturbance settings using data for parts of the Swedish railway network that currently experience capacity deficiencies. The evaluation has identified certain disturbances characteristics that have a significant influence on the disturbance propagation, and which in some cases complicate the re-scheduling procedure. Furthermore, the significance of applying certain re-scheduling objectives and their correlation with performance measures has been analysed. The analysis shows e.g. that a minimisation of accumulated delays has a tendency to delay more trains than a minimisation of total final delay or total delay costs. An experimental study of the long-term effects when applying a limited planning perspective has also been conducted. The results indicate that solutions which are good on longer-term can be achieved despite the use of a limited planning horizon. In parallel to the optimisation-based approaches, an agent-based conceptual model with emphasis on the interplay between the different components in the railway traffic system has been proposed.

  • 23. Törnquist, Johanna
    Railway traffic disturbance management — An experimental analysis of disturbance complexity, management objectives and limitations in planning horizon2007In: Transportation Research Part A: Policy & Practice, ISSN 0965-8564 , Vol. 41, no 3, p. 249-266Article in journal (Refereed)
  • 24. Törnquist, Johanna
    et al.
    Davidsson, Paul
    A Multi-Agent System Approach to Train Delay Handling2002Conference paper (Refereed)
  • 25. Törnquist, Johanna
    et al.
    Gustafsson, Inger
    Perceived benefits of improved information exchange: a case study on rail and multimodal transports2004In: Where theory and Practice Meet: Innovations and Case Studies in Assessing the Economic Impacts of ITS and Telematics, Elsevier Science , 2004, p. 415-440Chapter in book (Other academic)
  • 26. Törnquist, Johanna
    et al.
    Persson, Jan A.
    N-tracked railway traffic re-scheduling during disturbances2007In: Transportation Research Part B: Methodological, ISSN 0191-2615 , Vol. 41, no 3, p. 342-362Article in journal (Refereed)
  • 27. Törnquist, Johanna
    et al.
    Persson, Jan A.
    Train Traffic Deviation Handling Using Tabu Search and Simulated Annealing: A Swedish Case2005Conference paper (Refereed)
  • 28.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Computational decision-support for railway traffic management and associated configuration challenges: An experimental study2015In: Journal of Rail Transport Planning & Management, ISSN 2210-9706, Vol. 5, no 3, p. 95-109, article id 10.1016/j.jrtpm.2015.09.002Article in journal (Refereed)
    Abstract [en]

    This paper investigates potential configuration challenges in the development of optimization-based computational re-scheduling support for railway traffic networks. The paper presents results from an experimental study on how the characteristics of different situations influence the problem formulation and the resulting re-scheduling solutions. Two alternative objective functions are applied: Minimization of the delays at the end stations which exceed three minutes and minimization of delays larger than three minutes at intermediary commercial stops and at end stations. The study focuses on the congested, single-tracked Iron Ore line located in Northern Sweden. A combinatorial optimization model adapted to the special restrictions of this line is applied on 20 different disturbance scenarios and solved using commercial optimization software. The resulting re-scheduling solutions are analyzed numerically and visually in order to better understand the practical impact of using the suggested problem formulations in this context. The results show that the two alternative, objective functions result in structurally, quite different re-scheduling solutions. All scenarios were solved to optimality within 1 minute or less, which indicates that commercial solvers can handle practical problems of a relevant size for this type of setting, but the type of scenario has also a significant impact on the computation time.

  • 29.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, Faculty of Computing, Department of Computer Science and Engineering.
    Configuration of an optimization-based decision support for railway traffic management in different contexts2015In: 6th International Conference on Railway Operations Modelling and Analysis, Tokyo, March 23-26, 2015, 2015Conference paper (Refereed)
    Abstract [en]

    This paper investigates potential configuration challenges in the development of optimization-based computational re-scheduling support for railway traffic networks. The paper presents results from an experimental study on how the characteristics of different situations and the network influence the problem formulation and the resulting re-scheduling solutions. Two alternative objective functions are applied: a) Minimization of the delays at the end stations which exceed three minutes and b) minimization of delays larger than three minutes at intermediary commercial stops and at end stations. The study focuses on the congested, single-tracked Iron Ore line located in Northern Sweden and partially Norway. A combinatorial optimization model adapted to the special restrictions of this line is applied and solved using commercial optimization software. 20 different disturbance scenarios are solved and the resulting re-scheduling solutions are analyzed numerically and visually in order to better understand their practical impact. The results show that the two alternative, but similar, objective functions result in structurally, quite different re-scheduling solutions. The results also show that the selected objective functions have some flaws when it comes to scheduling trains that are ahead of their schedule by early departure, or by having a lot of margin time due to waiting time in meeting/passing locations. These early trains are not always “pushed” forward unless the objective function promotes that in some way. All scenarios were solved to optimality within 1 minute or less, which indicates that commercial solvers can handle practical problems of a relevant size for this type of setting.

  • 30.
    Zeeshan Iqbal, Syed Muhammad
    et al.
    Blekinge Institute of Technology, School of Computing.
    Grahn, Håkan
    Blekinge Institute of Technology, School of Computing.
    Törnquist Krasemann, Johanna
    Blekinge Institute of Technology, School of Computing.
    A Comparative Evaluation of Re-scheduling Strategies for Train Dispatching during Disturbances2012Conference paper (Refereed)
    Abstract [en]

    Railway traffic disturbances occur and train dispatchers make re-scheduling decisions in order to reduce the delays. In order to support the dispatchers, good rescheduling strategies are required that could reduce the delays. We propose and evaluate re-scheduling strategies based on: (i) earliest start time, (ii) earliest track release time, (iii) smallest buffer time, and (iv) shortest section runtime. A comparative evaluation is done for a busy part of the Swedish railway network. Our results indicate that strategies based on earliest start time and earliest track release time have the best average performance.

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