| 1. |
- 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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| 2. |
- Bohlin, Markus, et al.
(författare)
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Evaluation of planning policies for marshalling track allocation using simulation
- 2012. - 10
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Planning the operational procedures in a railway marshalling yard is a complex problem. When a train arrives at a marshalling yard, it is uncoupled on an arrival yard and then its cars are rolled to a classification yard. All cars should eventually be rolled to the classification track that has been assigned to the train they’re supposed to depart with. However, there is normally not enough capacity to compound all trains at once. In Sweden, cars arriving before a track has been assigned to their train can be stored on separate tracks called mixing tracks. All cars on mixing tracks will be pulled back to the arrival yard, and then rolled to the classification yard again to allow for reclassification. Today all procedures are planned by experienced dispatchers, but there are no documented strategies or guidelines for efficient manual planning. The aim of this paper is to examine operational planning strategies that could help dispatchers find a feasible marshalling schedule that minimizes unnecessary mixing. In order to achieve this goal, two different online planning strategies have been tested using deterministic and stochastic simulation. The Hallsberg marshalling yard was used as a case study, and was simulated for the time period between December 2010 and May 2011. The first tested strategy simply assigns tracks to trains on a first come-first served basis, while the second strategy uses time limits to determine when tracks should be assigned to departing trains. The online planning algorithms have been compared with an offline optimized track allocation. The results from both the deterministic and the stochastic simulation show that the optimized allocation is better than all online strategies and that the second strategy with a time limit of 32 hours is the best online method.
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| 3. |
- Bohlin, Markus, et al.
(författare)
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Hump Yard Track Allocation with Temporary Car Storage
- 2011. - 12
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Ingår i: 4th International Seminar on Railway Operations Modelling and Analysis.
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Konferensbidrag (refereegranskat)abstract
- In rail freight operation, freight cars need to be separated and reformed into new trains at hump yards. The classification procedure is complex and hump yards constitute bottlenecks in the rail freight network, often causing outbound trains to be delayed. One of the problems is that planning for the allocation of tracks at hump yards is difficult, given that the planner has limited resources (tracks, shunting engines, etc.) and needs to foresee the future capacity requirements when planning for the current inbound trains. In this paper, we consider the problem of allocating classification tracks in a rail freight hump yard for arriving and departing trains with predetermined arrival and departure times. The core problem can be formulated as a special list coloring problem. We focus on an extension where individual cars can temporarily be stored on a special subset of the tracks. An extension where individual cars can temporarily be stored on a special subset of the tracks is also considered. We model the problem using mixed integer programming, and also propose several heuristics that can quickly give feasible track allocations. As a case study, we consider a real-world problem instance from the Hallsberg Rangerbangård hump yard in Sweden. Planning over horizons over two to four days, we obtain feasible solutions from both the exact and heuristic approaches that allow all outgoing trains to leave on time.
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| 4. |
- Bohlin, Markus, et al.
(författare)
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Hump Yard Track Allocation with Temporary Car Storage
- 2010. - 11
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In rail freight operation, freight cars need to be separated and reformed into new trains at hump yards. The classification procedure is complex and time consuming, and hump yards often constitute bottlenecks in the rail freight network. One of the problems is that planning for the allocation of tracks at hump yards is difficult, given that the planner has limited resources (tracks, shunting engines, etc.) and needs to foresee the future capacity requirements when planning for the current inbound trains. In this paper, we consider the problem of allocating classification tracks in a rail freight hump yard for arriving and departing trains. Arrival and departure times are predetermined and may originate in timetables or estimated arrival and departure times (in case of disturbances in the rail system). The core problem can be formulated as a special list coloring problem. We focus on an extension where individual cars can temporarily be stored on a special subset of the tracks. We model the problem using mixed integer programming, and also propose several heuristics that can quickly give feasible track allocations. As a case study, we consider a real-world problem instance from the Hallsberg Rangerbangård hump yard in Sweden. Planning over horizons over two to four days, we obtain feasible solutions from both the exact and heuristic approaches that allow all outgoing trains to leave on time.
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| 5. |
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| 6. |
- Bohlin, Markus, et al.
(författare)
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Optimal Freight Train Classification using Column Generation
- 2012. - 9
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Ingår i: 12th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems, September 13, 2012, Ljubljana, Slovenia. - Dagstuhl, Germany : Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik. - 9783939897453 ; , s. 10-22
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Konferensbidrag (refereegranskat)abstract
- We consider planning of freight train classification at hump yards using integer programming. The problem involves the formation of departing freight trains from arriving trains subject to scheduling and capacity constraints. To increase yard capacity, we allow the temporary storage of early freight cars on specific mixed-usage tracks. The problem has previously been modeled using a direct integer programming model, but this approach did not yield lower bounds of sufficient quality to prove optimality. In this paper, we formulate a new extended integer programming model and design a column generation approach based on branch-and-price to solve problem instances of industrial size. We evaluate the method on historical data from the Hallsberg hump yard in Sweden, and compare the results with previous approaches. The new method managed to find optimal solutions in all of the 192 problem instances tried. Furthermore, no instance took more than 13 minutes to solve to optimality using fairly standard computer hardware.
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| 7. |
- Bohlin, Markus, et al.
(författare)
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Optimerad rangering: slutsatser och resultat från projektet RANPLAN
- 2013. - 7
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sammanfattning Rapporten innehåller kortfattade slutsatser och resultat från en studie genomförd i projektet RANPLAN, som har utförts av SICS Swedish ICT AB på uppdrag av Trafikverket under åren 2010-2013. Fokus är på Hallsbergs rangerbangård, men resultaten är tillämpbara även på andra rangerbangårdar med vall. Datorkörningar visar att blanddragen kan öka kapaciteten på rangerbangårdar väsentligt, mätt i antalet samtidiga tåg som kan hanteras, till en kostnad av en ökad mängd vagnsrörelser. I en jämförande datorstudie av simulering och optimering framgick också att de optimala planerna var betydligt effektivare, mätt i antalet vagnsrörelser, än de simulerade planerna. Resultaten pekar tydligt på att datorstödd optimering av planeringsprocessen för rangerbangårdar både är praktiskt möjligt och kan ge stora effektivitetsvinster.
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| 8. |
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| 9. |
- Bohlin, Markus, et al.
(författare)
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Optimized shunting with mixed-usage tracks
- 2013. - 16
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We consider the planning of railway freight classification at hump yards, where the problem involves the formation of departing freight train blocks from arriving trains subject to scheduling and capacity constraints. The hump yard layout considered consists of arrival tracks of sufficient length at an arrival yard, a hump, classification tracks of non-uniform and possibly non-sufficient length at a classification yard, and departure tracks of sufficient length. To increase yard capacity, freight cars arriving early can be stored temporarily on specific mixed-usage tracks. The entire hump yard planning process is covered in this paper, and heuristics for arrival and departure track assignment, as well as hump scheduling, have been included to provide the neccessary input data. However, the central problem considered is the classification track allocation problem. This problem has previously been modeled using direct mixed integer programming models, but this approach did not yield lower bounds of sufficient quality to prove optimality. Later attempts focused on a column generation approach based on branch-and-price that could solve problem instances of industrial size. Building upon the column generation approach we introduce a direct arc-based integer programming model, where the arcs are precedence relations between blocks on the same classification track. Further, the most promising models are adapted for rolling-horizon planning. We evaluate the methods on historical data from the Hallsberg shunting yard in Sweden. The results show that the new arc-based model performs as well as the column generation approach. It returns an optimal schedule within the execution time limit for all instances but from one, and executes as fast as the column generation approach. Further, the short execution times of the column generation approach and the arc-indexed model make them suitable for rolling-horizon planning, while the direct mixed integer program proved to be too slow for this. Extended analysis of the results shows that mixing was only required if the maximum number of concurrent trains on the classification yard exceeds 29 (there are 32 available tracks), and that after this point the number of extra car roll-ins increases heavily.
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| 10. |
- Bohlin, Markus, et al.
(författare)
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Searching for gas turbine maintenance schedules
- 2010
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Ingår i: The AI Magazine. - : Wiley. - 0738-4602. ; 31:1, s. 21-36
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Tidskriftsartikel (refereegranskat)abstract
- Preventive-maintenance schedules occurring in industry are often suboptimal with regard to maintenance coallocation, loss-of-production costs, and availability. We describe the implementation and deployment of a software decision support, tool for the maintenance planning of gas turbines, with the goal of reducing the direct maintenance costs and the often costly production losses during maintenance down time. The optimization problem is formally defined, and we argue that the feasibility version is NP-complete. We outline a heuristic algorithm that can quickly solve the problem for practical purposes and validate the approach on a real-world scenario based on an oil production facility. We also compare the performance of our algorithm with result's from using integer programming and d'iscuss the deployment of the application. The experimental results indicate that down time reductions up to 65 percent can be achieved, compared to traditional preventive maintenance. In addition, the use of our tool is expected to improve availability by up to 1 percent and to reduce the number of planned maintenance days by 12 percent. Compared to an integer programming approach, our algorithm is not optimal but is much faster and produces results that are useful in practice. Our test results and SIT AB's estimates based on operational use both indicate that significant savings can be achieved by using our software tool, compared to maintenance plans with fixed intervals.
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