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A Simulation-Optimization Approach for Improved Robustness of Railway Timetables
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.ORCID iD: 0000-0002-6479-5645
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The timetable is an essential part for the operations of railway traffic, and its quality is considered to have large impact on capacity utilization and reliability of the transport mode. The process of generating a timetable is most often a manual task with limited computer aid, and is known to be a complex planning problem due to inter-train dependencies.

These inter-train dependencies makes it hard to manually generate feasible timetables, and also makes it hard to improve a given timetable as new conflicts and surprising effects easily can occur.

As the demand for railway traffic is expected to continue grow, higher frequencies and more saturated timetables are required. However, in many European countries there is also an on-going public debate on the punctuality of the railway, which may worsen by increased capacity utilization. It is therefore also a need to increase the robustness of the services. This calls for increased precision of both the planning and the operation, which can be achieved with a higher degree of automation.

The research in this thesis is aimed at improving the robustness of railway timetables by combining micro-simulation with mathematical optimization, two methods that today are used frequently by practitioners and researchers but rarely in combination. In this research a sequential approach based on simulating a given timetable and re-optimizing it to reduce the weighted sum of scheduled travel time and predicted average delay is proposed. The approach has generated promising results in simulation studies, in which it has been possible to substantially improve the punctuality and reduce the average delays by only increasing the advertised travel times slightly. Further, the results have also indicated a positive socio-economic benefit. This demonstrates the methods potential usefulness and motivates further research.

Abstract [sv]

För järnvägen har tidtabellen en central roll, och dess kvalité har stor betydelse för kapacitet och tillförlitlighet. Processen att konstruera en tidtabell är ofta en uppgift som utförs manuellt med begränsat datorstöd och på grund av beroenden mellan enskilda tåg är det ofta ett tidskrävande och svårt arbete.

Dessa tågberoenden gör det svårt att manuellt konstruera konfliktfria tidtabeller samtidigt som det också är svårt att manuellt förbättra en given tidtabell, vilket beror på att de är svårt att förutsäga vad effekten av en given ändring blir.

Eftersom efterfrågan på järnväg fortsatt förväntas öka, finns det ett behov av att kunna köra fler tåg. Samtidigt pågår det redan i många europeiska länder en offentlig debatt om järnvägen punktlighet, vilken riskeras att försämras vid högre kapacitetsanvändning. Därför finns det även ett behov av att förbättra tidtabellernas robusthet, där robusthet syftar till en tidtabells möjlighet att stå emot och återhämta mindre förseningar. För att hantera denna målkonflikt kommer det behövas ökad precision vid både planering och drift, vilket kan uppnås med en högre grad av automation.

Forskningen i denna avhandling syftar till att förbättra robustheten för tågtidtabeller genom att kombinera mikro-simulering med matematisk optimering, två metoder som redan används i hög grad av både yrkesverksamma trafikplanerare och forskare men som sällan kombineras. I den här avhandlingen förslås en sekventiell metod baserad på att simulera en given tidtabell och optimera den för att minska den viktade summan av planerad restid och predikterad medelförsening. Metoden har visat på lovande resultat i simuleringsstudier, där det har varit möjligt att uppnå en väsentligt bättre punktlighet och minskad medelförsening, genom att endast förlänga de planerade restiderna marginellt. Även förbättrad samhällsekonomisk nytta har observerats av att tillämpa den föreslagna metoden. Sammantaget visar detta metodens potentiella nytta och motiverar även fortsatt forskning.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2019. , p. 29
Series
TRITA-ABE-DLT ; 1942
Keywords [en]
Railroad, Timetabling, Optimization, Simulation, Robustness, Punctuality, Delay prediction.
Keywords [sv]
Järnväg, Tidtabelläggning, Optimering, Simulering, Robusthet, Punktlighet, Förseningsprediktion.
National Category
Transport Systems and Logistics
Research subject
Transport Science; Transport Science, Transport Systems
Identifiers
URN: urn:nbn:se:kth:diva-263761ISBN: 978-91-7873-364-4 (print)OAI: oai:DiVA.org:kth-263761DiVA, id: diva2:1369596
Presentation
2019-12-04, B26, Brinellvägen 23, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Transport Administration, TRV 2016/5090
Note

QC 20191112

Available from: 2019-11-12 Created: 2019-11-12 Last updated: 2019-12-10Bibliographically approved
List of papers
1. Combining Optimization and Simulation to Improve Railway Timetable Robustness
Open this publication in new window or tab >>Combining Optimization and Simulation to Improve Railway Timetable Robustness
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The Train Timetabling Problem (TTP) is the problem of finding the timetable that utilizes the infrastructure as efficient as possible, while satisfying market demands and operational constraints. As reliability is important to passengers it is important that timetables are robust. In this paper we propose a method that combines optimization and simulation to find the timetable that minimizes the travel times and maximizes the expected punctuality. The core method consists of iteratively re-optimizing a bi-objective mixed integer sequencing timetable model, where both planned travel time and simulated delays are taken into account. Each generated timetable is validated and re-evaluated using the micro-simulation tool RailSys. The advantage of the method is that it captures both the uncertainty of a timetable at the planning stage and the validity of the generated timetable. The method is evaluated on a unidirectional track section of the Western Main Line in Sweden and shows promising results for future research.

Keywords
Railway timetabling, Robustness, Optimization, Simulation, Punctuality
National Category
Transport Systems and Logistics
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-262872 (URN)
Conference
7th International Conference on Railway Operations Modelling and Analysis (RailLille 2017), Lille, France, April 4th-7th 2017
Funder
Swedish Transport Administration, TRV 2016/5090
Note

QC 20191022

Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-12Bibliographically approved
2. A combined simulation-optimization approach for minimizing travel time and delays in railway timetables
Open this publication in new window or tab >>A combined simulation-optimization approach for minimizing travel time and delays in railway timetables
2019 (English)In: Transportation Research Part B: Methodological, ISSN 0191-2615, E-ISSN 1879-2367, Vol. 126, p. 192-212Article in journal (Refereed) Published
Abstract [en]

Minimal travel time and maximal reliability are two of the most important properties of a railway transportation service. This paper considers the problem of finding a timetable for a given set of departures that minimizes the weighted sum of scheduled travel time and expected delay, thereby capturing these two important socio-economic properties of a timetable. To accurately represent the complex secondary delays in operational railway traffic, an approach combining microscopic simulation and macroscopic timetable optimization is proposed. To predict the expected delay in the macroscopic timetable, a surrogate function is formulated, as well as a subproblem to calibrate the parameters in the model. In a set of computational experiments, the approach increased the socio-economic benefit by 2-5% and improved the punctuality by 8-25%.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Railroad, Robustness, Optimization, Simulation, Punctuality
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-257557 (URN)10.1016/j.trb.2019.04.003 (DOI)000478708800009 ()2-s2.0-85067307580 (Scopus ID)
Note

QC 20190924

Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-11-12Bibliographically approved
3. Delay Prediction with Flexible Train Order in a MILP Simulation-Optimization Approach for Railway Timetabling
Open this publication in new window or tab >>Delay Prediction with Flexible Train Order in a MILP Simulation-Optimization Approach for Railway Timetabling
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper considers the problem of minimizing travel times and maximizing travel time reliability, which are important socio-economic properties of a railway transport service, for a given set of departures on a double-track line. In this paper travel time reliability is measured as the average delay, and a delay prediction model for MILP timetable optimization is presented. The average delay prediction model takes into consideration time supplements, buffer times and propagation of delays in the railway network and is not restricted to a fixed order of the trains. Validation of the average delay prediction model, and an evaluation of the approach with combined simulation-optimization for improving railway timetables, are conducted by a simulation study on a part of the Swedish Southern Main Line. Results from the simulation study show that the average delays are reduced by up to approximately 40% and that the punctuality is improved by up to approximately 8%.

Place, publisher, year, edition, pages
Linköping: , 2019
Series
Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 69
Keywords
Timetabling, Optimization, Simulation, Delay prediction, Robustness, Punctuality
National Category
Transport Systems and Logistics
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-262874 (URN)978-91-7929-992-7 (ISBN)
Conference
RailNorrköping 2019. 8th International Conference on Railway Operations Modelling and Analysis (ICROMA), Norrköping, Sweden, June 17th – 20th, 2019
Funder
Swedish Transport Administration, TRV 2016/5090
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-12Bibliographically approved

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