| 1. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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A disaggregate bundle method for train timetabling problems
- 2020
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In: Journal of Rail Transport Planning & Management. - : Elsevier BV. - 2210-9706 .- 2210-9714. ; 16
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Are commuter train timetables consistent with passengers’ valuations of waiting times and in-vehicle crowding?
- 2020
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Reports (other academic/artistic)abstract
- Many models have been developed and used to analyse the costs and benefits of transport investments. Similar tools can also be used for transport operation planning and capacity allocation. An example of such use is the assessment of commuter train operations and service frequency. In this study, we analyse the societally optimal frequency for commuter train services. The aim is to reveal the implicit valuation (by the public transport agency) of the waiting time and the in-vehicle crowding in the commuting system. We use an analytic CBA model to formulate the societal costs of a certain service frequency and analyse the societally optimal frequencies during peak and off-peak hours. Comparing the optimal and the actual frequencies allows to reveal the implicit valuations of waiting time and crowding. Using relevant data from the commuter train services in Stockholm on a typical working day in September 2015 (e.g., OD matrix, cost parameters), we perform a numerical analysis on certain lines and directions. We find the societally optimal frequency and the implicit valuation of waiting time and crowding. The results suggest that the public transport agency in Stockholm (i.e., SL) adopted service frequencies that are generally slightly higher than societally optimum which can be explained by a higher implicit valuation of waiting time and crowding. We also find that the optimal frequencies are more sensitive to the waiting time valuation rather than that of crowding.
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| 3. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Are commuter train timetables consistent with passengers’ valuations of waiting times and in-vehicle crowding?
- 2022
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In: Transport Policy. - : Elsevier BV. - 0967-070X .- 1879-310X. ; 116, s. 188-198
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Assessing Innovations in High-Speed Rail Infrastructure
- 2023
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In: Socioeconomic Impacts of High-Speed Rail Systems - Proceedings of the 2nd International Workshop on High-Speed Rail Socioeconomic Impacts, IW-HSR 2022. - Stockholm : Springer Nature. ; , s. 217-233, s. 217-233
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Conference paper (peer-reviewed)abstract
- Innovations in high-speed rail (HSR) have had substantial effects on different stakeholders within and outside the railway system. As part of the European Shift2Rail research programme, several innovative solutions are developed for, among others, improving the HSR infrastructure. The Joint Undertaking behind this research program has set objectives for these innovations in terms of punctuality, capacity, and life cycle costs. With a focus on infrastructure-related innovations for HSR, this paper aims at assessing their impacts in relation to these targets. We review the relevant research literature about the effects of HSR innovations and their assessment. The paper presents a hybrid assessment methodology combing different approaches to assess capacity, punctuality, and cost effects. This contributes to reducing the existing gap that is found in the research literature. Based on a reference scenario for HSR line and collected data from different stakeholders, the results indicate that infrastructure innovations in HSR, being developed within the European Shift2Rail research programme, can contribute to reaching the target set for punctuality. Further innovations in HSR infrastructure and/or other railway assets may be needed to reach additional targets and for more accurate improvement values giving more insights into their impacts.
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| 5. |
- Ait-Ali, Abderrahman, 1991-
(author)
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Assessing the Use of Welfare-Based Track Access Charging for Railway Capacity Allocation
- 2019
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Conference paper (other academic/artistic)abstract
- The deregulation of railway markets has brought new challenges to the capacity allocation process. In this context, we present a new hybrid methodology for allocating railway capacity to commercial train operators. Commercial freight or passenger train operators compete with each other as well as with subsidised local commuter trains. In the method presented in this article, minimal track access charges are computed using a social cost-benefit analysis of alternative commuter train timetables. These minimal charges are used as a starting or reservation price in an auction-based method for capacity allocation between the commercial operators. The aim of this study is to assess the use of such a welfare-based track access charging system in a real case scenario. On a congested line in the region of Stockholm, we evaluate the welfare-based access charges of commercial operators. We show that the new methodology can be used to allocate capacity between subsidized and commercial train operators. Moreover, we provide an estimate of the marginal minimal access charge per train path that the commercial operators request.
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| 6. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Disaggregation in Bundle Methods : Application to the Train Timetabling Problem
- 2017
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Conference paper (peer-reviewed)abstract
- Bundle methods are often used to solve dual problems that arise from Lagrangian relaxations of large scale optimization problems. An example of such problems is the train timetabling problem. This paper focuses on solving a dual problem that arises from Lagrangian relaxation of a train timetabling optimization program. The dual problem is solved using bundle methods. We formulate and compare the performances of two different bundle methods: the aggregate method, which is a standard method, and a new, disaggregate, method which is proposed here. The two methods were tested on realistic train timetabling scenarios from the Iron Ore railway line. The numerical results show that the new disaggregate approach generally yields faster convergence than the standard aggregate approach.
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| 7. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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European Railway Deregulation : An overview of market organization and capacity allocation
- 2022
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In: Transportmetrica A. - : Taylor & Francis. - 2324-9935 .- 2324-9943. ; 18:3, s. 594-618
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Evaluating the mix of maintenance activities on railway crossings with respect to life-cycle costs
- 2023
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Reports (other academic/artistic)abstract
- 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.
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| 9. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Evaluating the mix of maintenance activities on railway crossings with respect to life-cycle costs
- 2024
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In: Sammanställning av referat från Transportforum 2024. - Linköping : Statens väg- och transportforskningsinstitut. ; , s. 405-406
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Conference paper (other academic/artistic)abstract
- Switches and crossings (S&Cs) are critical assets in the Swedish rail infrastructure, with a density of 0.8 S&C per track-km and renewal costs of up to 4.5 million SEK/S&C. The efficiency of maintenance strategies for S&Cs is vital from a (socio-)economic perspective. The focus of this study is on the importance of the mix of maintenance activities performed on a S&C with respect to its life-cycle costs (LCCs). The study investigates the interdependencies between the deterioration mechanisms, preventive and corrective maintenance activities, and expected LCCs, including transportation costs due to traffic disruptions/delays. One or a combination of different approaches are often used in the literature, such as engineering or LCC methods. In this research, a novel approach is introduced that combines mechanical simulations, data analysis, econometrics, and LCC calculations to compare the efficiency of different maintenance strategies. The mechanical simulations consider one S&C on the Swedish railway network. The selection criteria were that the S&C is located on the main line, installed in 2014 (generates the longest observation period given the availability of data), and had no extreme values with respect traffic volume, maintenance activities and failures. The interrelation between the degradation of contact geometry and track settlement is analysed using simulations of dynamic vehicle–turnout interaction. Further, the relationship between frequency of preventive and occurrence of corrective maintenance activities is analyses using an econometric model. Implications of a specific mix of maintenance activities on the S&C lifetime and LCC are evaluated using different cost parameters. Results obtained from mechanical simulations reveal the correlation between poor crossing geometry and higher rates of ballast settlement. The econometric analysis finds a statistically significant impact of (cumulative) preventive maintenance on corrective maintenance, i.e., more preventive maintenance leads to fewer corrective activities. Based on a standard mix of maintenance activities (inferred using econometric regression across all S&Cs), the lifetime of the selected S&C is estimated to 10 years with a lower associated LCC than that resulting from the record of performed maintenance activities at the site. The LCC evaluations highlight the potential to improve the efficiency of S&C maintenance by adopting proactive strategies.
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| 10. |
- Ait Ali, Abderrahman, 1991-, et al.
(author)
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Evaluation of long-term maintenance of switches & crossings with respect to life-cycle costs and socio-economic impact
- 2022
-
Conference paper (other academic/artistic)abstract
- 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, and they can cause major delays and disruptions if they are not well maintained. This motivates studies to improve maintenance strategies of S&Cs, considering both life-cycle costs (LCC) of the assets and other additional socio-economic costs (e.g., 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. Changes in the timing of the associated maintenance measures (crossing repair welding and tamping) are performed to investigate the impact on damage modes. This is then linked to LCC and transportation costs, which requires a distribution between preventive and corrective activities with respect to the simulated maintenance strategy. This relationship is investigated by means of regression modelling: ??????????=?(??????????,?)where Corrective and Preventive represent the number of failures and the scheduled actions to prevent these failures, respectively. ? holds variables related to the traffic (volume, type of traffic, axle load, etc.) and the infrastructure (type of S&Cs, etc.).
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