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| 2. |
- Andersson, Emma, 1983-, et al.
(författare)
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Improved Railway Timetable Robustness for Reduced Traffic Delays – a MILP approach
- 2015
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Ingår i: 6th International Conference on Railway Operations Modelling and Analysis, Tokyo, Mars 23-26, 2015..
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Konferensbidrag (refereegranskat)abstract
- Maintaining high on-time performance and at the same time having high capacity utilization is a challenge for several railway traffic systems. The system becomes sensitive to disturbances and delays are easily propagating in the network. One way to handle this problem is to create more robust timetables; timetables that can absorb delays and prevent them from propagating. This paper presents an optimization approach to reduce the propagating of delays with a more efficient margin allocation in the timetable. A Mixed Integer Linear Programming (MILP) model is proposed in which the existing margin time is re-allocated to increase the robustness for an existing timetable. The model re-allocates both runtime margin time and headway margin time to increase the robustness at specific delay sensitive points in a timetable. We illustrate the model’s applicability for a real-world case where an initial, feasible timetable is modified to create new timetables with increased robustness. These new timetables are then evaluated and compared to the initial timetable. We evaluate how the MILP approach affects the initial timetable structure and its capability to handle disturbances by exposing the initial and the modified timetables to some minor initial disturbances of the range 1 up to 7 minutes. The results show that it is possible to reduce the delays by re-allocating margin time, for example, the total delay at end station decreases with 28 % in our real-world example.
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| 3. |
- Andersson, Emma, 1983-, et al.
(författare)
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Introducing a New Quantitative Measure of Railway Timetable Robustness Based on Critical Points
- 2013
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Ingår i: 5th International Seminar on Railway Operations Modelling and Analysis - RailCopenhagen 2013. - 9788773272466
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Konferensbidrag (refereegranskat)abstract
- The growing demand for railway capacity has led to high capacity consumption at times and a delay-sensitive network with insufficient robustness. The fundamental challenge is therefore to decide how to increase the robustness. To do so there is a need for accurate measures that return whether the timetable is robust or not and indicate where improvements should be made. Previously presented measures are useful when comparing different timetable candidates with respect to robustness, but less useful to decide where and how robustness should be inserted. In this paper, we focus on points where trains enter a line, or where trains are being overtaken, since we have observed that these points are critical for the robustness. The concept of critical points can be used in the practical timetabling process to identify 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 RCP (Robustness in Critical Points). A high RCP value is preferred, and it reflects a situation at which train dispatchers will have higher prospects of handling a conflict effectively. The number of critical points, the location pattern and the RCP values constitute an absolute value for the robustness of a certain train slot, as well as of a complete timetable. The concept of critical points and RCP can be seen as a contribution to the already defined robustness measures which combined can be used as guidelines for timetable constructors.
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| 4. |
- Andersson, Emma, et al.
(författare)
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Robustness in Swedish Railway Traffic Timetables
- 2011
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Ingår i: Railrome 2011.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A tendency seen for quite some time in the Swedish railway network is a growing demand for capacity which no longer can be accommodated. This causes congestion and delays, and the relationships between the trains and how they affect eachother are significantly harder to overview and analyse. Railway traffic timetables normally contain margins to make them robust, and enable trains to recover from certain delays. How effective these margins are, depends on their size and location as well as the frequency and magnitude of the disturbances that occur. Hence, it is important to include marigns so, that they can be used operationally to recover from a variety of disturbances and not restricted to a specific part of the line and/or the timetable. In a case study we compare the performance of a selection of passenger train services to the different prerequisites given by the timetable (e.g. available margins and their location, critical train dependencies). The study focuses on the Swedish Southern mainline between Stockholm and Malmö on which a wide variety of train services operate, e.g. freight trains, local and regional commuter train services as well as long-distance trains with different speed profiles. The analysis shows a clear mismatch between where margins are placed and where delays occur. We also believe that the most widely used performance measure, which is related to the delay when arriving at the final destination, might give rise to an unnecessarily high delay rate at intermediate stations.
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| 5. |
- Andersson, Emma V.
(författare)
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Assessment of Robustness in Railway Traffic Timetables
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A tendency seen for the last decades in many European railway networks is a growing demand for capacity. An increased number of operating trains has led to a delay sensitive system where it is hard to recover from delays, where even relatively small delays are easily propagating to other traffic.The overall aim of this thesis is to analyse the robustness of railway traffic timetables; why delays are propagating in the network and how the timetable design and dispatching strategies influence the delays. In this context we want to establish quantitative measures of timetable robustness. There is a need for measures that can be used by the timetable constructors. Measures that identify where and how to improve the robustness and thereby indicating how and where margin time should be inserted. It is also important that the measures can capture interdependencies between different trains.In this thesis we introduce the concept of critical points, which is a practical approach to identify robustness weaknesses in a timetable. In contrast to other measures, critical points can be used to identify specific locations in both time and space. The corresponding measure, Robustness in Critical Points (RCP) provides the timetable constructors with concrete suggestions for which trains that should be given more runtime or headway margin. The measure also identifies where the margin time should be allocated to achieve a higher robustness.In a case study we show that the delay propagation is highly related to the operational train dispatching. This study shows that the current prioritisation rule used in Sweden results in an economic inefficiency and therefore should be revised. This statement is further supported by RCP and the importance of giving the train dispatchers more flexibility to efficiently solve conflict situations.
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| 6. |
- Andersson, Emma V., 1983-, et al.
(författare)
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Quantifying railway timetable robustness in critical points
- 2013
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Ingår i: Journal of Rail Transport Planning and Management. - : Elsevier. - 2210-9706 .- 2210-9714. ; 3:3, s. 95-110
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 7. |
- Backåker, Lars, 1984-
(författare)
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The Influence of Customer Agreements and Planning Principles on Rail Freight Performance
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rail freight transportation is recognized worldwide as a suitable transportation mode when it comes to long haul transportation of heavy commodities. The industry is also known to be capital intensive, highly dependent on infrastructural developments and requires thorough planning of operations. Despite intensive planning of operations, great challenges remain in how to make best use of existing resources. Especially uncertainties related to up-coming daily freight volumes stand as central causes behind such planning challenges. This thesis focuses on rail freight carload transportation and concerns how customer commitments influence operational performance as well as potentials for improvements of operational planning principles. Problem statements are addressed using three separate studies and all experiments involve quantitative approaches. The first study investigates effects of a potential Volume Variation Allowance (VVA) policy through simulation. The policy dictates how much freight volumes are allowed to vary by day of week. Results indicate that effects of the policy are relatively small, but an overall decrease in transportation times is observed. The study also identifies improvement potentials with respect to the current operational planning principles used within Swedish railways. The second study proposes a new optimization-based approach for trip plan generation. The approach, including a number of extensions, is evaluated against the current industry practice. Results confirm the potentials for reduced transportation times, shunting activities as well as service frequencies. All experiments satisfy existing customer commitments. The third study explores effects of a Fixed Carload Capacity (FCC) concept which partially allows capacity reservation on services. The study adopts an extension of the previously developed optimization approach. Results confirm the hypothetical trade-off between customer groups and the dependency on capacity reservation levels, but indicate that the concept has relatively small effects with respect to regular carload customers. On the other hand, benefits in terms of guarantee of service and reliability in transportation times can be observed for the customer under the agreement.
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| 8. |
- Carlson, Annelie, 1969-, et al.
(författare)
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Nuvarande förutsättningar och försök med längre godståg mellan Gävle och Malmö
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Andra delprojektet av ELVIS-demonstrationsprojektet för längre och tyngre godståg syftar till att analysera dagens förutsättningar för användningen av längre tåg och att utvärdera demonstrationsförsöket där ett 730 meter långt demonstrationståg (i stället för dagens maximala 630 meter) kördes mellan Gävle och Malmö 6–7 oktober 2012. En slutsats är att det är tekniskt möjligt att trafikera tåg som är längre än 630 meter men det finns organisatoriska hinder. För att utnyttja infrastrukturen effektivare, föreslår projektet som en temporär lösning användningen av dedikerade kanaler för längre godståg i specifika korridorer. Jämförelsen av demonstrationstågets färd med upp till 630 meter långa referenståg, försvårades mycket av att centrala data som beskriver referenstågen var svåra att få tag på och delvis osäkra. En viktig slutsats är att det behövs en bättre kartläggning av nuläget för att kunna göra tillförlitliga kvantitativa analyser. Det var möjligt att sammanställa information om elförbrukningen per bruttotonkilometer för demonstrationståget och 85 referenståg. Däremot är det svårt att kvantifiera hur exakt tågens längd, vikt, hastighet och antal stopp med mera, påverkar elförbrukningen var för sig – både med hänsyn till det bristfälliga datamaterialet och det faktum att det finns en relativt stor variation i elförbrukningen oavsett vilken aspekt som studerats. Betydelse av topografin och tågets längd och vikt för elförbrukningen per bruttotonkilometer kan visas. Demonstrationstågets elförbrukning per bruttotonkilometer är generellt sett lågt i jämförelse med referenstågen. Det går dock att dra slutsatsen att elförbrukningen per bruttotonkilometer generellt inte är högre för längre tåg men det går inte att säga att förbrukningen generellt är lägre. Litteraturen och diskussioner med företagen indikerar att näringslivets transportkostnader per transporterat ton gods kan reduceras genom att använda längre godståg. Skalfördelarna kan dock enbart utnyttjas om inte hela lokets dragkraft utnyttjas redan idag. Det är uppenbart att den tillgängliga järnvägsinfrastrukturen avgör vilka tåglängder och -vikter som är affärsmässigt gångbara. Elkostnaderna per transporterat ton kan möjligtvis också reduceras genom att använda längre tåg, men detta kan inte förutsättas utan vidare. En trafikering av längre godståg i större omfattning kräver investeringar i mötesspår, förbigångsspår, terminalspår med mera. De hittills genomförda överslagsmässiga kalkylerna för 750 meter långa tåg tyder på att investeringskostnaderna är relativt blygsamma. Det finns behov av analyser för olika tåglängder eftersom det inte är uppenbart att minimilängden på 750 meter, som krävs på TEN-T:s stomnät från 2030, är optimal.
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| 9. |
- Davidsson, Paul, et al.
(författare)
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Agent-Based Approaches to Transport Logistics
- 2004
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Davidsson, Paul, et al.
(författare)
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An Analysis of Agent-Based Approaches to Transport Logistics
- 2005
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Ingår i: Transportation Research Part C: Emerging Technologies. - : Elsevier. - 0968-090X. ; 13:4, s. 255-271
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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