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Ait Ali, AbderrahmanORCID iD iconorcid.org/0000-0001-9535-0617
Biography [eng]

The main research project that I am currently working on is SamEff (Samhällsekonomiskt effektiv tilldelning av järnvägskapacitet) which translates to Socio-economically efficient railway capacity allocation. It aims at improving the railway capacity allocation in Sweden using cost benefit analysis, mathematical programming and welfare-economics. I also work with operations research methods (e.g. mathematical programming) for OD-estimation and train timetabling.

Biography [swe]

Mitt huvudsakliga forskningsprojekt är SamEff (Samhällsekonomiskt effektiv tilldelning av järnvägskapacitet). Syftet är att förbättra järnvägskapacitetstilldelningen i Sverige med hjälp av samhällsekonomiska kalkyler, trafikmodellering och välfärdsekonomi. Jag jobbar också med operationsanalytiska metoder (t ex matematisk programmering) för OD-estimering och tågtidtabell.

Publications (8 of 8) Show all publications
Ait Ali, A., Eliasson, J. & Warg, J. (2022). Are commuter train timetables consistent with passengers' valuations of waiting times and in-vehicle crowding?. Transport Policy, 116, 188-198
Open this publication in new window or tab >>Are commuter train timetables consistent with passengers' valuations of waiting times and in-vehicle crowding?
2022 (English)In: Transport Policy, ISSN 0967-070X, E-ISSN 1879-310X, Vol. 116, p. 188-198Article in journal (Refereed) Published
Abstract [en]

Social cost-benefit analysis is often used to analyse transport investments, and can also be used for transport operation planning and capacity allocation. If it is to be used for resolving capacity conflicts, however, it is important to know whether transit agencies' timetable requests are consistent with the cost-benefit framework, which is based on passenger preferences. We show how a public transport agency's implicit valuations of waiting time and crowding can be estimated by analysing timetables, apply the method to commuter train timetables in Stockholm, and compare the implicit valuations to the corresponding passenger valuations in the official Swedish cost-benefit analysis guidelines. The results suggest that the agency puts a slightly lower value on waiting time and crowding than the passenger valuations codified in the official guidelines. We discuss possible reasons for this and implications for using cost-benefit analysis for capacity allocation. We also find that optimal frequencies are more sensitive to the waiting time valuation than to that of crowding.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Waiting time, Crowding, Cost-benefit analysis, Implicit preference, Commuter train
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-181610 (URN)10.1016/j.tranpol.2021.11.025 (DOI)000751667100001 ()
Projects
SamEff
Funder
Swedish Transport Administration
Note

Funding: Swedish Transport Administration (Trafikverket) [samhadllsekonomiskt effektiv tilldelning av kapacitet pa jadrnvadgar]

Available from: 2021-12-03 Created: 2021-12-03 Last updated: 2023-01-10Bibliographically approved
Ait Ali, A. & Eliasson, J. (2022). European Railway Deregulation: An overview of market organization and capacity allocation. Transportmetrica A: Transport Science, 18(3), 594-618
Open this publication in new window or tab >>European Railway Deregulation: An overview of market organization and capacity allocation
2022 (English)In: Transportmetrica A: Transport Science, ISSN 2324-9935, E-ISSN 2324-9943, Vol. 18, no 3, p. 594-618Article in journal (Refereed) Published
Abstract [en]

Railway markets in Europe have been reorganized to allow competition between different operators. Thus, European railways have been vertically separated, separating infrastructure management from provisions of train services. This allows several train operators to compete for passengers and freight services. Different ways have emerged for vertical separation, capacity allocation and track access charges. This paper reviews, compares and discusses important deregulation aspects, using examples from a number of European countries to show different possible solutions. The study describes how competition has been introduced and regulated, with a particular focus on describing the different ways capacity is allocated and how conflicting requests by different train operators are resolved. It also reviews the related issue of how access charges are constructed and applied. Although guided by the same European legislation, we conclude that the studied railways have different deregulation outcomes, e.g., market organization, capacity allocation. Besides, few countries have so far managed to create efficient and transparent processes for allocating capacity between competing train operators. Although allowed by the legislation, market-based allocation is absent or never used. In order to foster more competition which can yield substantial social benefits, the survey indicates that most European railways still need to develop and experiment with more efficient and transparent capacity allocation procedures.

Place, publisher, year, edition, pages
Taylor & Francis, 2022
Keywords
Railway deregulation, Vertical separation, Competition, Capacity allocation, Access charges
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-173445 (URN)10.1080/23249935.2021.1885521 (DOI)000621709500001 ()
Note

Funding: This research is part of the project Socio-economically efficient allocation of railway capacity, SamEff (Samhallsekonomiskt effektiv tilldelning av kapacitet pa jarnvagar) which is funded by a grant from the Swedish Transport Administration (Trafikverket). The authors are grateful to Jan-Eric Nilsson and Yves Crozet for reference recommendations as well as Russell Pittman, Steven Harrod, Roger Pyddoke and several anonymous reviewers for the valuable discussions and comments.

Available from: 2021-02-19 Created: 2021-02-19 Last updated: 2022-10-17
Ait Ali, A. & Eliasson, J. (2022). The value of additional data for public transport origin–destination matrix estimation. Public Transport, 14(2), 419-439
Open this publication in new window or tab >>The value of additional data for public transport origin–destination matrix estimation
2022 (English)In: Public Transport, ISSN 1866-749X, E-ISSN 1613-7159, Vol. 14, no 2, p. 419-439Article in journal (Refereed) Published
Abstract [en]

Passenger origin–destination data is an important input for public transport planning. In recent years, new data sources have become increasingly common through the use of the automatic collection of entry counts, exit counts and link flows. However, collecting such data can be sometimes costly. The value of additional data collection hence has to be weighed against its costs. We study the value of additional data for estimating time-dependent origin–destination matrices, using a case study from the London Piccadilly underground line. Our focus is on how the precision of the estimated matrix increases when additional data on link flow, destination count and/or average travel distance is added, starting from origin counts only. We concentrate on the precision of the most policy-relevant estimation outputs, namely, link flows and station exit flows. Our results suggest that link flows are harder to estimate than exit flows, and only using entry and exit data is far from enough to estimate link flows with any precision. Information about the average trip distance adds greatly to the estimation precision. The marginal value of additional destination counts decreases only slowly, so a relatively large number of exit station measurement points seem warranted. Link flow data for a subset of links hardly add to the precision, especially if other data have already been added.

Place, publisher, year, edition, pages
Springer, 2022
Keywords
Dynamic origin-destination; OD estimation; entropy maximization; lagrangian relaxation; smart card; public transport
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-179343 (URN)10.1007/s12469-021-00282-0 (DOI)000695756100001 ()
Projects
SamEff
Funder
Swedish Transport Administration
Note

Funding: Swedish National Road and Transport Research Institute (VTI); Swedish Transport Administration (Trafikverket)

Available from: 2021-09-19 Created: 2021-09-19 Last updated: 2022-10-14
Ait Ali, A., Lindberg, P. O., Eliasson, J., Nilsson, J.-E. & Peterson, A. (2020). A disaggregate bundle method for train timetabling problems. Journal of Rail Transport Planning & Management, 16, Article ID 100200.
Open this publication in new window or tab >>A disaggregate bundle method for train timetabling problems
Show others...
2020 (English)In: Journal of Rail Transport Planning & Management, ISSN 2210-9706, E-ISSN 2210-9714, Vol. 16, article id 100200Article in journal (Refereed) Published
Abstract [en]

The train timetabling problem (TTP) consists of finding a feasible timetable for a number of trains which minimises some objective function, e.g., sum of running times or deviations from ideal departure times. One solution approach is to solve the dual problem of the TTP using so-called bundle methods. This paper presents a new bundle method that uses disaggregate data, as opposed to the standard bundle method which in a certain sense relies on aggregate data. We compare the disaggregate and aggregate methods on realistic train timetabling scenarios from the Iron Ore line in Northern Sweden. Numerical results indicate that the proposed disaggregate method reaches better solutions faster than the standard aggregate approach.

Keywords
Train timetabling, Disaggregation, Bundle methods, Lagrangian relaxation, Mathematical programming
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-165781 (URN)10.1016/j.jrtpm.2020.100200 (DOI)000597313000002 ()
Projects
SamEff
Funder
Swedish Transport Administration
Note

The accepted version is also available on the author's home page: 

http://abdeaitali.github.io/

Funding agencies: Swedish Transport Administration (Trafikverket)

Available from: 2020-05-24 Created: 2020-05-24 Last updated: 2021-12-01
Ait Ali, A. (2020). Methods for Capacity Allocation in Deregulated Railway Markets. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Methods for Capacity Allocation in Deregulated Railway Markets
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Faced with increasing challenges, railways around Europe have recently undergone major reforms aiming to improve the efficiency and competitiveness of the railway sector. New market structures such as vertical separation, deregulation and open access can allow for reduced public expenditures, increased market competition, and more efficient railway systems.

However, these structures have introduced new challenges for managing infrastructure and operations. Railway capacity allocation, previously internally performed within monopolistic national companies, are now conferred to an infrastructure manager. The manager is responsible for transparent and efficient allocation of available capacity to the different (often competing) licensed railway undertakings.

This thesis aims at developing a number of methods that can help allocate capacity in a deregulated (vertically separated) railway market. It focuses on efficiency in terms of social welfare, and transparency in terms of clarity and fairness. The work is concerned with successive allocation of capacity for publicly controlled and commercial traffic within a segmented railway market.

The contributions include cost benefit analysis methods that allow public transport authorities to assess the social welfare of their traffic, and create efficient schedules. The thesis also describes a market-based transparent capacity allocation where infrastructure managers price commercial train paths to solve capacity conflicts with publicly controlled traffic. Additionally, solution methods are developed to help estimate passenger demand, which is a necessary input both for resolving conflicts, and for creating efficient timetables.

Future capacity allocation in deregulated markets may include solution methods from this thesis. However, further experimentations are still required to address concerns such as data, legislation and acceptability. Moreover, future works can include prototyping and pilot projects on the proposed solutions, and investigating legal and digitalisation strategies to facilitate the implementation of such solutions.

Abstract [sv]

Med ökande utmaningar har järnvägar runt om i Europa genomgått stora reformer som syftar till att förbättra järnvägssektorns effektivitet och konkurrenskraft. Nya marknadsstrukturer såsom vertikal separering, avreglering och öppet tillträde för flera operatörer kan möjliggöra minskade offentliga kostnader, ökad marknadskonkurrens och effektivare järnvägssystem.

Denna omreglering av järnvägsmarknaderna har dock skapat nya utmaningar för hanteringen av järnvägsinfrastruktur och drift. Tilldelning av järnvägskapacitet, vilket tidigare sköttes inom nationella monopolföretag, måste nu göras av en infrastrukturförvaltare (infrastructure manager). Förvaltarens kapacitetstilldelning till olika (ofta konkurrerande) licensierade järnvägsföretag (railway undertakings) måste samtidigt vara transparent, rättvis och leda till ett effektivt kapacitetsutnyttjande.

I denna avhandling utvecklas metoder som kan användas av en infrastrukturförvaltare för att tilldela kapacitet i en avreglerad järnvägsmarknad. Den fokuserar på samhällsekonomiskt effektiva utfall men även transparens, tydlighet och rättvisa.

Avhandlingens bidrag omfattar samhällsekonomiska analysmetoder som gör det möjligt för regionala kollektivtrafikmyndigheter att bedöma den samhällsekonomiska effektiviteten för deras trafikering och skapa ett effektivt utbud. Med dessa metoder som utgångspunkt beskrivs en marknadsbaserad och transparent tilldelningsprocess för kapacitet där infrastrukturförvaltare prissätter kommersiella tåglägen för att lösa kapacitetskonflikter med offentligt kontrollerad trafik. Dessutom utvecklas optimeringsmetoder för att estimera passagerarefterfrågan och för att skapa effektiva tågtidtabeller.

Framtida kapacitetstilldelning på avreglerade marknader kan inkludera lösningsmetoder från denna avhandling. Ytterligare experiment krävs dock fortfarande för att hantera problem såsom data, lagstiftning och godtagbarhet. Dessutom kan framtida arbete omfatta prototyper och pilotprojekt av de föreslagna lösningarna och undersöka lagliga och digitaliseringsstrategier för att underlätta implementeringen av sådana lösningar.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2020. p. 51
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2101
Keywords
railway capacity, capacity allocation, train timetable, cost benefit analysis, deregulated market, spårkapacitet, kapacitetstilldelning, tågtidtabell, samhällsekonomisk analys, avreglerad marknad
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-170193 (URN)10.3384/diss.diva-170193 (DOI)9789179297718 (ISBN)
Public defence
2020-11-16, Online through Zoom (contact abderrahman.ait.ali@liu.se) and TPM51, Täppan, Campus Norrköping, Norrköping, 13:15 (English)
Opponent
Supervisors
Available from: 2020-10-01 Created: 2020-10-01 Last updated: 2021-12-03Bibliographically approved
Ait Ali, A., Warg, J. & Eliasson, J. (2020). Pricing commercial train path requests based on societal costs. Transportation Research Part A: Policy and Practice, 132, 452-464
Open this publication in new window or tab >>Pricing commercial train path requests based on societal costs
2020 (English)In: Transportation Research Part A: Policy and Practice, ISSN 0965-8564, E-ISSN 1879-2375, Vol. 132, p. 452-464Article in journal (Refereed) Published
Abstract [en]

On deregulated railway markets, efficient capacity allocation is important. We study the case where commercial trains and publicly controlled traffic (“commuter trains”) use the same railway infrastructure and hence compete for capacity. We develop a method that can be used by an infrastructure manager trying to allocate capacity in a socially efficient way. The method calculates the loss of societal benefits incurred by changing the commuter train timetable to accommodate a commercial train path request, and based on this calculates a reservation price for the train path request. If the commercial operator’s willingness-to-pay for the train path exceeds the loss of societal benefits, its request is approved. The calculation of these benefits takes into account changes in commuter train passengers’ travel times, waiting times, transfers and crowding, and changes in operating costs for the commuter train operator(s). The method is implemented in a microscopic simulation program, which makes it possible to test the robustness and feasibility of timetable alternatives. We show that the method is possible to apply in practice by demonstrating it in a case study from Stockholm, illustrating the magnitudes of the resulting commercial train path prices. We conclude that marginal societal costs of railway capacity in Stockholm are considerably higher than the current track access charges.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Train timetables, Train conflicts, Capacity pricing, Railway capacity, Capacity allocation
National Category
Economics
Identifiers
urn:nbn:se:liu:diva-162784 (URN)10.1016/j.tra.2019.12.005 (DOI)000514014700030 ()2-s2.0-85076736383 (Scopus ID)
Projects
SamEff
Note

Funding agencies:  Swedish Transport Administration (Trafikverket) [Samhallsekonomiskt effektiv tilldelning av kapacitet pa jarnvagar]

The accepted version is also available on the author's home page: 

http://abdeaitali.github.io/

Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2021-12-01Bibliographically approved
Warg, J., Ait Ali, A. & Eliasson, J. (2019). Assessment of Commuter Train Timetables Including Transfers. In: Bernhard Friedrich, Dirk C. Mattfeld, Anysia Mayerhofer, Bruno Albert Neumann Saavedra (Ed.), Special Issue: 21st EURO Working Group on Transportation Meeting, EWGT 2018, 17th – 19th September 2018, Braunschweig, Germany: . Paper presented at 21st EURO Working Group on Transportation Meeting, EWGT 2018, 17th – 19th September 2018 (pp. 11-18). , 37
Open this publication in new window or tab >>Assessment of Commuter Train Timetables Including Transfers
2019 (English)In: Special Issue: 21st EURO Working Group on Transportation Meeting, EWGT 2018, 17th – 19th September 2018, Braunschweig, Germany / [ed] Bernhard Friedrich, Dirk C. Mattfeld, Anysia Mayerhofer, Bruno Albert Neumann Saavedra, 2019, Vol. 37, p. 11-18Conference paper, Published paper (Refereed)
Abstract [en]

Many railway networks suffer from high capacity utilisation. For scheduling all services, adjustments to the desired slots are often needed. Such adjustments might lead to longer travel times, crowded trains, longer waiting times for boarding and for transfers. All of this has an important socio-economic impact on both travellers and train operators. This raises the question of the socio-economic assessment of changes in commuter train timetables including transfers. Thus, the aim of this study is to evaluate the effects of adjustments of commuter train timetables on the traveller (i.e. consumer costs) and the train operator (i.e. producer costs). These costs are estimated based on all train trips and operations in the network. In a case study, the effect of changes in departure times (resulting in non-regular interval timetables) is analysed. Further, the price of cancelling a two-way service during different times of the day is compared. The results show that changing departure times can both decrease and increase the total costs, and that regularity for parallel services might not be as important as expected if it is kept for each separate service. For the second study, waiting times for transfers were indicated to have a (too) large impact which can lead to misleading results and might be adjusted in future work. The model is adequate for such kind of questions but needs some more adjustments. For railway networks with dense and heterogeneous traffic (as is the case in Sweden), the contributions of this model are useful for making the challenging timetabling process easier and commuter train services less costly.

Series
Transportation Research Procedia, E-ISSN 2352-1457
Keywords
train timetablingsocio-economic assessmentregular interval timetablescancelled trainstransfer
National Category
Transport Systems and Logistics
Research subject
Economic Information Systems
Identifiers
urn:nbn:se:liu:diva-165780 (URN)10.1016/j.trpro.2018.12.160 (DOI)000471043300002 ()2-s2.0-85062233024 (Scopus ID)
Conference
21st EURO Working Group on Transportation Meeting, EWGT 2018, 17th – 19th September 2018
Projects
SamEff
Funder
Swedish Transport Administration
Available from: 2020-05-24 Created: 2020-05-24 Last updated: 2024-01-29
Ait Ali, A., Eliasson, J. & Warg, J. (2017). Measuring the Socio-economic Benefits of Train Timetables: Application to Commuter Train Services in Stockholm. In: Domokos Esztergár-Kiss, Tamás Mátrai, János Tóth, István Varga (Ed.), : . Paper presented at 20th EURO Working Group on Transportation Meeting (pp. 849-856). , 27
Open this publication in new window or tab >>Measuring the Socio-economic Benefits of Train Timetables: Application to Commuter Train Services in Stockholm
2017 (English)In: / [ed] Domokos Esztergár-Kiss, Tamás Mátrai, János Tóth, István Varga, 2017, Vol. 27, p. 849-856Conference paper, Published paper (Refereed)
Abstract [en]

On highly used railway lines with heterogeneous traffic, timetabling is challenging. In particular, the limited existing capacity means that to guarantee an acceptable level of quality, the infrastructure manager must cancel some train services on the expense of others. In this article, we study the conflict between commercial long-distance trains and subsidized commuter trains with a socio-economic perspective (i.e. travelers and train operators). The study attempts to answer the following question: What is the socio-economic effect of modifying the timetable of a commuter service?

The case study treats the commuter train services in Stockholm. Trip data was collected from the local commuter train operator. An entropy maximization-based model was implemented to estimate the dynamic network Origin-Destination (OD) matrix. This dynamic matrix, of one full working day, was then used to estimate the number of travelers per train, and further converted for use in the microscopic simulation tool RailSys. Travel and waiting time are estimated for each OD pair and with that the generalized costs for the travelers and operators. The effect of crowding in the trains is included in the estimation. The article can be considered as an initiation to a novel method to calculate effects of changes in commuter train timetables. This novel approach enables to price commercial train slots in the capacity allocation process such as in an auction. It provides a new way to estimate the local train operator´s valuation of the different parameters (i.e. waiting, travel time and interchanges). Using RailSys for the estimation of times makes it possible to include capacity aspects that normally are difficult to reveal.

Series
Transportation Research Procedia, ISSN 2352-1465
Keywords
Train Timetabling, Socio-economic benefits, Railway simulation
National Category
Transport Systems and Logistics
Research subject
Economic Information Systems
Identifiers
urn:nbn:se:liu:diva-165782 (URN)10.1016/j.trpro.2017.12.124 (DOI)
Conference
20th EURO Working Group on Transportation Meeting
Projects
SamEff
Funder
Swedish Transport Administration
Available from: 2020-05-24 Created: 2020-05-24 Last updated: 2021-12-01
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9535-0617