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Ait-Ali, AbderrahmanORCID iD iconorcid.org/0000-0001-9535-0617
Alternative names
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 (10 of 15) Show all publications
Torstensson, P., Hossein-Nia, S., Ait Ali, A., Odolinski, K., Larsson Kråik, P.-O., Krishna, V. & Sundholm, L. (2024). LCC evaluation of rail maintenance strategies using simulations of long-term mechanical degradation. In: Fredrik Hellman; Mattias Haraldsson (Ed.), Sammanställning av referat från Transportforum 2024: . Paper presented at Transportforum, Linköping, Sweden, January 17-18, 2024. (pp. 408-409). Linköping: Statens väg- och transportforskningsinstitut
Open this publication in new window or tab >>LCC evaluation of rail maintenance strategies using simulations of long-term mechanical degradation
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2024 (English)In: Sammanställning av referat från Transportforum 2024 / [ed] Fredrik Hellman; Mattias Haraldsson, Linköping: Statens väg- och transportforskningsinstitut , 2024, p. 408-409Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Rail infrastructure is an important part of transport systems, improving accessibility and contributing to economic growth. This requires costly maintenance and renewal activities that are subject to budget constraints. There is a need to carry out the right activity at the right time to make best use of limited resources. This paper proposes a methodology to evaluate the performance of different rail grinding strategies from a life cycle cost (LCC) perspective. The procedure is innovative in such a way that it uses simulations of long-term mechanical degradation with respect to different maintenance interventions and combines these simulations with an assessment of the associated economic impact. The utilisation of mechanical modelling makes the procedure able to analyse new/innovative maintenance strategies or changes in infrastructure/vehicle design, as well as to perform optimisation and parameter studies under controlled conditions.   

The proposed methodology for LCC evaluation is applied to compare the performance of different maintenance strategies on a 495 m radius curve on the Iron-ore line in Sweden. The traffic consists of freight trains containing two back-to-back connected three-axle locomotives and 67 wagons on three-piece bogies. The annual traffic volume is around 37 mega gross tonnes (MGT) corresponding to around 20 train passages each day, half (un)loaded, with 30 tonnes axle load. 

Three different maintenance strategies are investigated; (S1) the currently applied strategy on the Iron-ore line corresponding to rail grinding performed biannually on rail material R350LHT, (S2) rail grinding performed annually on rail material R400HT, and (S3) the same as (S1) but with gauge width correction performed to prevent it from exceeding 1450 mm.  

Long-term rail profile evaluation due to mechanical degradation and rail grinding is assessed by iterative simulations of dynamic vehicle–track interaction in the software GENSYS. Rail damage due to wear and rolling contact fatigue are modelled in accordance with Archard’s theory and the method by KTH, respectively.  

Place, publisher, year, edition, pages
Linköping: Statens väg- och transportforskningsinstitut, 2024
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-204980 (URN)
Conference
Transportforum, Linköping, Sweden, January 17-18, 2024.
Available from: 2024-04-04 Created: 2024-06-18
Ait Ali, A. & Peterson, A. (2024). Värdering av trafikinformationsnyttor i tågtrafiken (VTT): slutrapport. Trafikverket
Open this publication in new window or tab >>Värdering av trafikinformationsnyttor i tågtrafiken (VTT): slutrapport
2024 (Swedish)Report (Other academic)
Abstract [sv]

Tågförseningar tillsammans med ökande efterfrågan leder till betydande sociala kostnader. Ett sätt att minska dessa kostnader är genom effektiv kommunikation av olika typer av trafikinformation till passagerare. Beroende på vilken/när information tas emot minskar passagerarnas beteendeanpassningar deras resekostnader, särskilt vid förseningar.Detta projekt syftar till att beräkna de samhällsekonomiska nyttor som sådan trafikinformation ger. Detta åstadkoms genom att utveckla en kvantitativ modell för att kvantifiera värdet av att kommunicera information till resenärerna vid tågförseningar.Genom att studera olika störningsscenarier i ett studiefall från Stockholmspendeltåg, ger studien insikter till infrastrukturförvaltaren om samhällsnytta av sådana informationssystem som en del av de stora infrastrukturinvesteringarna. Dessa insikter kan också hjälpa till att utforma effektivare informationsstrategier för att minska samhällsekonomiska kostnader för tågstörningar. 

Abstract [en]

Train delays with increasing demand result in substantial social costs. One way to reduce these costs is through efficient communication of various types of traffic information to passengers. Depending on which/when information is received, passengers’ behavioral adaptations reduce their travel costs especially in the event of delays.This project aims at calculating the social benefits of such traffic information. The purpose is to develop a quantitative model to quantify the value of communicating information to passengers in cases of train delays.Using different disruption scenarios in a case study from Stockholm commuter train services, the study provides insights to the infrastructure manager on the social value of such information systems as part of the large infrastructure investments. These insights can also help design more effective information strategies to reduce social costs of train disruptions.

Place, publisher, year, edition, pages
Trafikverket, 2024. p. 19
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-204979 (URN)
Funder
Swedish Transport Administration
Available from: 2024-06-18 Created: 2024-06-18 Last updated: 2024-06-18
Odolinski, K., Nilsson, J.-E., Sjöstrand, H., Ait Ali, A. & Lidén, T. (2023). Att följa upp och utvärdera järnvägsunderhåll: Delrapport inom projektet Metod för jämförelsestudier av järnvägsunderhåll. Linköping: Statens väg- och transportforskningsinstitut
Open this publication in new window or tab >>Att följa upp och utvärdera järnvägsunderhåll: Delrapport inom projektet Metod för jämförelsestudier av järnvägsunderhåll
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2023 (Swedish)Report (Other academic)
Alternative title[en]
Monitoring and evaluating railway maintenance : Interim report of the projectMethodology for comparative studies of railway maintenance
Abstract [sv]

Med start 2025 avser Trafikverket förändra formerna för upphandling av basunderhåll i tre geografiska områden. Förändringarna innebär att en större mängd planering och produktionsledning sker i Trafikverkets regi. Syftet är att utveckla den egna beställarförmågan och att stärka leverantörsmarknaden.

VTI har fått Trafikverkets uppdrag att föreslå metoder för att kunna följa upp konsekvenserna av den förändrade organisationen. I rapporten redovisas uppdragets första del med fokus på konsekvenserna av ett förändrat ansvar för basunderhåll av Södra Malmbanan. Syftet med delstudien är att identifiera den information som krävs och de metoder som kommer att användas för att fördjupa förståelsen av hur den nya ansvarsfördelningen förändrar kostnader och förutsättningarna för trafik jämfört med dagens förfarande. Förutom att skapa goda förutsättningar att utvärdera de förändringar som genomförs kommer detta arbete också att kunna ge stöd för övergången till nya verksamhetsupplägg i de ytterligare två områden som står på tur att förändras, Ostkustbanan (2026) och Mälarbanan (2027). Information har inhämtats från personal inom Trafikverket och från aktörer på leverantörsmarknaden, samt via analyser av dokumentationen av underhållsverksamheten liksom en genomgång av relevant litteratur.

De betydande förändringar av verksamheten som förestår kan få konsekvenser i flera avseenden. För att kunna följa upp och jämföra kostnader och andra utfall i hela landet krävs uppgifter från samtliga kontraktsområden med avseende på verksamhetens kostnader, omfattning (antal kilometer bana, installationer av växlar och konstbyggnader), trafik, väder etcetera. Tack vare att Trafikverket sedan länge byggt upp databaser som innehåller den aktuella informationen är en viktig del av det fortsatta arbetet att etablera ett smidigt tillvägagångssätt för att årligen kunna komplettera informationen och göra nya observationer av förändringar som kan ha inträffat. Ett antal frågeställningar föreslås som kan besvaras med stöd av en analys av det föreslagna materialet. Svaret på dessa frågor gör det möjligt att stärka förståelsen av den verksamhet som bedrivs och att ta fram kunskap som kan omsättas i praktiken.

Place, publisher, year, edition, pages
Linköping: Statens väg- och transportforskningsinstitut, 2023. p. 57
Keywords
Underhåll, järnväg, egen regi, upphandling, effektivitet, beställarkunskap
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:liu:diva-204984 (URN)
Funder
Swedish Transport Administration, 2023/4028
Available from: 2024-06-18 Created: 2024-06-18 Last updated: 2024-06-18
Ait Ali, A., Odolinski, K., Pålsson, B. & Torstensson, P. (2023). Evaluating the mix of maintenance activities on railway crossings with respect to life-cycle costs. Stockholm: Statens väg- och transportforskningsinstitut
Open this publication in new window or tab >>Evaluating the mix of maintenance activities on railway crossings with respect to life-cycle costs
2023 (English)Report (Other academic)
Abstract [en]

Switches & crossings (S&Cs) are vital assets as they allow for increased railway capacity by introducing flexibility and connectivity in railway networks. At the same time, this makes them critical since they can cause costly delays and disruptions if they are not well maintained. This motivates studies to improve maintenance strategies of S&Cs, considering both the life-cycle costs (LCC) of the assets and socio-economic transportation costs for passengers and freight customers. In this paper, the interdependence between deterioration mechanisms, maintenance activities, and expected LCC (including transportation costs) is investigated using a combination of mechanical and econometric modelling. The interrelation between the degradation of contact geometry and track settlement is analysed using simulations of dynamic vehicle–turnout interaction. Long-term mechanical degradation of the S&C is simulated for different maintenance strategies that correspond to different timing of the associated maintenance measures (crossing repair welding and tamping). This provides the basis for analysing the interdependence between preventive and corrective activities using econometric modelling. Based on a case study of a common type of S&Cs in the Swedish infrastructure, the impact of different maintenance strategies on LCC and transportation costs is analysed. Opportunities and challenges in the development of more socio-economically effective maintenance strategies of S&Cs are discussed.

Place, publisher, year, edition, pages
Stockholm: Statens väg- och transportforskningsinstitut, 2023. p. 28
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:liu:diva-204983 (URN)
Available from: 2024-06-18 Created: 2024-06-18 Last updated: 2024-06-18
Odolinski, K., Nissen, A. & Ait Ali, A. (2023). Finding a better renewal time and improved contract design for switches and crossings. Stockholm: VTI
Open this publication in new window or tab >>Finding a better renewal time and improved contract design for switches and crossings
2023 (English)Report (Other academic)
Abstract [en]

Switches and crossings are critical assets in railway systems and their maintenance and renewal costs can be substantial. This paper evaluates the economic impact of cumulative loads on such assets and the effect of different contract designs for railway maintenance. Results from survival analyses are combined with a life cycle costing model to analyse costs for maintenance, train delays, and renewals. The findings provide insights into improving the timing of asset renewal as well as the impact of different reimbursement rules in the design of maintenance contracts. The estimated optimal lifetimes of different types of switches and crossings are similar to their technical lifetimes, yet there a couple of exceptions. The estimated effects of the reimbursement rule provide unique results on the risk premiums allowed in order to achieve a break-even between different maintenance contract designs.

Place, publisher, year, edition, pages
Stockholm: VTI, 2023. p. 33
National Category
Infrastructure Engineering Economics
Identifiers
urn:nbn:se:liu:diva-204982 (URN)
Available from: 2024-06-18 Created: 2024-06-18 Last updated: 2024-06-18
Nia, S. H., Krishna, V. V., Odolinski, K., Torstensson, P., Ait Ali, A., Sundholm, L., . . . Stichel, S. (2023). Simulation-based evaluation of maintenance strategies from a life cycle cost perspective. Paper presented at The 12th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM 2022). Held in Melbourne, Australia from 4-7 September 2022. Wear, 532-533, 258-265, Article ID 205120.
Open this publication in new window or tab >>Simulation-based evaluation of maintenance strategies from a life cycle cost perspective
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2023 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 532-533, p. 258-265, article id 205120Article in journal (Refereed) Published
Abstract [en]

A methodology that combines simulations of long-term mechanical degradation including maintenance interventions with an assessment of the associated socio-economic impact is proposed. This development responds to an urgent need within the railway sector to enable the evaluation of maintenance strategies from a LCC perspective. The functionality of the methodology is demonstrated in an investigation of rail grinding strategies for a curve on the Swedish Iron-ore line. The results indicate a reduction in LCC of 20% when using a harder rail material (R400HT) combined with annual rail grinding as compared to a softer rail material (R350LHT) and two grinding campaigns per year.

Place, publisher, year, edition, pages
Elsevier, 2023
National Category
Vehicle and Aerospace Engineering Infrastructure Engineering
Identifiers
urn:nbn:se:liu:diva-204985 (URN)10.1016/j.wear.2023.205120 (DOI)2-s2.0-85149182015 (Scopus ID)9780646865881 (ISBN)
Conference
The 12th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM 2022). Held in Melbourne, Australia from 4-7 September 2022
Available from: 2024-06-18 Created: 2024-06-18 Last updated: 2025-02-14
Hossein-Nia, S., Ait Ali, A., Odolinski, K., Torstensson, P. & Stichel, S. (2023). Simulation-based evaluation of maintenance strategies using look-up tables. In: : . Paper presented at The 28th International Symposium on Dynamics of Vehicles on Roads and Tracks (IAVSD), Ottawa, Canada, 21-25 August 2023.
Open this publication in new window or tab >>Simulation-based evaluation of maintenance strategies using look-up tables
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2023 (English)Conference paper, Oral presentation only (Other academic)
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:liu:diva-204981 (URN)
Conference
The 28th International Symposium on Dynamics of Vehicles on Roads and Tracks (IAVSD), Ottawa, Canada, 21-25 August 2023
Available from: 2023-08-23 Created: 2024-06-18
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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9535-0617