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Urban transportation contributes significantly to CO2 emissions. Public transport systems are a good strategy to reduce these, but the emissions generated by public transport vehicles should not be neglected during the design of the service. The Transit Network Design and Frequency Setting Problem (TNDFSP) has usually been addressed considering only the passengers’ and the operator’s point of view. However, we show it is worthwhile to consider also the emissions already during this planning phase. This paper proposes a memetic algorithm to address the bi-objective TNDFSP where both the total travel time and the CO2 emissions are minimized. The analysis considers a heterogeneous fleet, meaning that buses of different sizes and technologies can be assigned under a budget constraint. The results on benchmark instances show that the proposed memetic algorithm performs as well as state-of-the-art algorithms where CO2 emissions are not considered. In addition, several experiments are carried out to observe the effect of incorporating emissions and heterogeneous fleet into the model. The heterogeneous fleet allows reducing travel times and emissions at the same time, compared to solutions without a heterogeneous fleet. Moreover, the explicit minimization of CO2 emissions within a bi-objective framework allows illustrating the trade-off between both objectives. Reductions of about 30% in the emissions can be achieved by increasing the travel time only 1%, while the costs for the operator remain the same. This clearly demonstrates the benefits of considering both the CO2 emissions and a heterogeneous fleet during the design stage of public transport systems. ispartof: European Journal Of Operational Research vol:282 issue:2 pages:580-592 status: published

© 2018 Elsevier Ltd In a railway system, a conflict occurs when two trains require the same part of the infrastructure at the same time. Currently, such conflicts are typically resolved manually by experienced dispatchers. However, it is impossible for them to fully anticipate the impact of their actions on the entire network. This paper proposes a conflict prevention strategy which focuses only on the relevant part of the network and traffic and, consequently, proposes a solution for that part only. The proposed strategy first looks for possible rerouting options by using an optimization model. If no solution is found, a solution based on delaying one of the trains is required. This retiming/reordering heuristic uses information from an offline calculation, for determining related conflicts that frequently occur. In this way, a so-called dynamic impact zone is created online for each conflict. When deciding which train to delay, the potential conflicts and the incurred delays of all trains in this dynamic impact zone are taken into account. The performance of this new Conflict Prevention Strategy is compared to a common dispatching strategy, other heuristics, and an exact method. Extensive experiments on a large part of the Belgian railway network show that by considering this dynamic impact zone the total delay can be decreased by at least 67% compared to the basic First Come, First Served decision rule. Moreover, the dynamic impact zone has a reasonable size and scales well to large networks as only the relevant conflicts and their expected consequences are considered. This makes our Dynamic Impact Zone heuristic very fast. The computation time for returning a resolution to a conflict with the proposed conflict prevention strategy is, for 95% of the conflicts, less than two seconds, and at most 26 s, including the creation of the dynamic impact zone of the conflict. ispartof: Transportation Research Part B vol:111 issue:111 pages:39-59 status: published

Planned infrastructure works reduce the available capacity of a railway system and make it more vulnerable to conflicts and delay propagation. The starting point of this paper is a published timetable that needs to be adapted due to the temporary unavailability of some resources. Since the timetable is in operation, changed arrival or departure times and cancelations have an impact on the passengers who need to adapt their travel behavior. In the light of passenger service, a trade-off is made between these inconveniences and the delays that occur in practice due to the reduced capacity. Taking the robustness of the adapted railway timetable into account is a new approach to rescheduling in case of a planned infrastructure unavailability. In this paper, an algorithm that adjusts the train routing and the train schedule to the planned maintenance interventions and keeps the level of passenger service as high as possible is presented. To avoid large inconveniences, the developed algorithm tries to minimize the number of cancelations. Computational results show that by allowing small modifications to the routing and the timetable, the robustness of the resulting solution can improve by more than 10 percent and only few trains need to be canceled. publisher: Elsevier articletitle: An iterative approach for reducing the impact of infrastructure maintenance on the performance of railway systems journaltitle: European Journal of Operational Research articlelink: http://dx.doi.org/10.1016/j.ejor.2015.12.037 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved. ispartof: European Journal of Operational Research vol:252 issue:1 pages:39-53 status: published

In order to improve the robustness of a railway system in station areas, this paper introduces an iterative approach to successively optimize the train routing through station areas and to enhance this solution by applying some changes to the timetable in a tabu search environment. We present our vision on robustness and describe how this vision can be used in practice. By introducing the spread of the trains in the objective function for the route choice and timetabling module, we improve the robustness of a railway system. Using a discrete event simulation model, the performance of our algorithms is evaluated based on a case study for the Brussels' area. The computational results indicate an average improvement in robustness of 6.2% together with a decrease in delay propagation of about 25%. Furthermore, the effect of some measures like changing the train offer to further increase the robustness is evaluated and compared. publisher: Elsevier articletitle: Improving the robustness in railway station areas journaltitle: European Journal of Operational Research articlelink: http://dx.doi.org/10.1016/j.ejor.2013.10.062 content_type: article copyright: Copyright © 2013 Elsevier B.V. All rights reserved. ispartof: European Journal of Operational Research vol:235 issue:1 pages:276-286 status: published

In this paper, we consider complex, busy stations whose limited capacity is one of the main reasons of delay propagation. Our goal is to improve, during the planning phase, the robustness of a complex station by fully exploiting the potential of the available capacity. The main feature of our approach is the interaction between routing decisions, timetabling and platform assignments. By altering one of these, slack can be created to allow improvements by the others as well. An objective function that maximizes the time span between any two trains is defined and the timing of the trains and the way how trains are routed to the platforms are optimized in the scope of this objective. By maximizing the spread of the trains, potential conflicts are avoided which is beneficial for - but not identical to - robustness. Using our approach, the robustness in the station zone of Brussels, Belgium's main railway bottleneck, can be improved by 8%. Next to that, the amount of knock-on delay arising due to conflicts within this area can be halved. This performance of our approach is confirmed by a second case study based on the station zone of Antwerp. Young Railway Operations Research Award 2013 of IAROR. ispartof: pages:1-20 ispartof: 5th International Seminar on Railway Operations Modelling and Analysis - RailCopenhagen pages:1-20 ispartof: 5th International Seminar on Railway Operations Modelling and Analysis - RailCopenhagen location:Copenhagen, Denmark date:13 May - 15 May 2013 status: published

During the last decade, a number of challenging applications in logistics, tourism and other fields were modelled as orienteering problems (OP). In the orienteering problem, a set of vertices is given, each with a score. The goal is to determine a path, limited in length, that visits some vertices and maximises the sum of the collected scores. In this paper, the literature about the orienteering problem and its applications is reviewed. The OP is formally described and many relevant variants are presented. All published exact solution approaches and (meta)heuristics are discussed and compared. Interesting open research questions concerning the OP conclude this paper. ispartof: European Journal of Operational Research vol:209 issue:1 pages:1-10 status: published