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Konstantinos Gkiotsalitis
Centre for Transport Studies, Department of Civil Engineering, University of Twente, Enschede, The Netherlands

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Journal article
Published: 16 April 2021 in Journal of Traffic and Transportation Engineering (English Edition)
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In high-frequency bus services, maintaining the service regularity is a critical issue. The service regularity is directly related to the excessive waiting times (EWT) of passengers at bus stops. In a regular service, the EWT is minimized resulting in even headways between consecutive buses of the same line. In this study, we propose the combined use of rescheduling and bus holding to improve passengers' excessive waiting times. We model the dynamic rescheduling and bus holding problem as an integer nonlinear program (INLP) and we prove its NP-hardness. Our model considers the constraints of the original timetable – an issue that is usually neglected from most dynamic control methods. Given the NP-hardness of our mathematical program, we introduce a problem-specific heuristic to explore efficiently the solution space. The convergence rate of the proposed heuristic is tested against other solution methods, including simulated annealing with linear cooling, hill climbing and branch and bound with multi-start sequential quadratic programming. In addition, simulations with the use of actual operational data from a major bus operator in Asia Pacific demonstrate an up to 35% potential EWT improvement for a minor increase of 6% to the travel times of onboard passengers.

ACS Style

Konstantinos Gkiotsalitis. Improving service regularity for high-frequency bus services with rescheduling and bus holding. Journal of Traffic and Transportation Engineering (English Edition) 2021, 1 .

AMA Style

Konstantinos Gkiotsalitis. Improving service regularity for high-frequency bus services with rescheduling and bus holding. Journal of Traffic and Transportation Engineering (English Edition). 2021; ():1.

Chicago/Turabian Style

Konstantinos Gkiotsalitis. 2021. "Improving service regularity for high-frequency bus services with rescheduling and bus holding." Journal of Traffic and Transportation Engineering (English Edition) , no. : 1.

Journal article
Published: 07 April 2021 in Transportation Research Part C: Emerging Technologies
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The availability of railway networks is important for society and the economy. To keep the infrastructure in good condition, regular maintenance is needed. Regular maintenance is achieved by devising maintenance schedules that assign safe work zones to crews executing preventive maintenance activities. This study aims to optimize the maintenance schedules for both train operators and maintenance contractors, by considering (a) hindrance for parked passenger trains and planned freight trains, and (b) the workload for track workers. Further, maintenance operations are distinguished into different engineering fields (switches, straight tracks, and overhead wiring) since this influences the amount of hindrance. The method presented for designing maintenance schedules is a novel mixed-integer linear programming (MILP) model that considers these aspects. In our Dutch case study, we assess our new scheduling model and show that large improvements can be made in terms of mean workload for work crews and total hindrance for train operators. We also assess the computational costs when using exact (branch-and-bound) or metaheuristic solution methods for solving networks with up to 25 work zones.

ACS Style

F. Nijland; K. Gkiotsalitis; E.C. van Berkum. Improving railway maintenance schedules by considering hindrance and capacity constraints. Transportation Research Part C: Emerging Technologies 2021, 126, 103108 .

AMA Style

F. Nijland, K. Gkiotsalitis, E.C. van Berkum. Improving railway maintenance schedules by considering hindrance and capacity constraints. Transportation Research Part C: Emerging Technologies. 2021; 126 ():103108.

Chicago/Turabian Style

F. Nijland; K. Gkiotsalitis; E.C. van Berkum. 2021. "Improving railway maintenance schedules by considering hindrance and capacity constraints." Transportation Research Part C: Emerging Technologies 126, no. : 103108.

Journal article
Published: 29 March 2021 in Future Transportation
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The COVID-19 pandemic has had an enormous impact on the public transport sector. After the start of the pandemic, passenger demand dropped significantly for public transport services. In addition, social distancing measures have resulted in introducing pandemic-imposed capacity limitations to public transport vehicles. Consequently, public transport operators should adjust their planning to minimize the impact of the COVID-19 pandemic. This study introduces a mixed-integer quadratic program that sets the optimal frequencies of public transport lines and sublines in order to conform with the pandemic-imposed capacity. The focus is on cases where the public transport demand is high, but the crowding levels inside public transport vehicles should remain below the pandemic-imposed capacities. Of particular interest are public transport lines with skewed demand profiles that can benefit from the introduction of short-turning sublines that serve the high-demand line segments. The frequency setting model is tested on a network containing two high-demand bus lines in the Twente region in the Netherlands, and it demonstrates that the revenue losses due to social distancing can be reduced when implementing short-turning service patterns.

ACS Style

Yoran de Weert; Konstantinos Gkiotsalitis. A COVID-19 Public Transport Frequency Setting Model That Includes Short-Turning Options. Future Transportation 2021, 1, 3 -20.

AMA Style

Yoran de Weert, Konstantinos Gkiotsalitis. A COVID-19 Public Transport Frequency Setting Model That Includes Short-Turning Options. Future Transportation. 2021; 1 (1):3-20.

Chicago/Turabian Style

Yoran de Weert; Konstantinos Gkiotsalitis. 2021. "A COVID-19 Public Transport Frequency Setting Model That Includes Short-Turning Options." Future Transportation 1, no. 1: 3-20.

Journal article
Published: 04 March 2021 in Transportation Research Interdisciplinary Perspectives
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As public transport operators try to resume their services, they have to operate under reduced capacities due to COVID-19. Because demand can exceed capacity at different areas and across different times of the day, drivers have to refuse passenger boardings at specific stops to avoid overcrowding. Given the urgent need to develop decision support tools that can prevent the overcrowding of vehicles, this study introduces a dynamic integer nonlinear program to derive the optimal service patterns of individual vehicles that are ready to be dispatched. In addition to the objective of satisfying the imposed vehicle capacity due to COVID-19, the proposed service pattern model accounts for the waiting time of passengers. Our model is tested in a bus line connecting the University of Twente with its surrounding cities demonstrating the trade-off between the reduced in-vehicle crowding levels and the excessive waiting times of unserved passengers.

ACS Style

K. Gkiotsalitis. A model for modifying the public transport service patterns to account for the imposed COVID-19 capacity. Transportation Research Interdisciplinary Perspectives 2021, 9, 100336 .

AMA Style

K. Gkiotsalitis. A model for modifying the public transport service patterns to account for the imposed COVID-19 capacity. Transportation Research Interdisciplinary Perspectives. 2021; 9 ():100336.

Chicago/Turabian Style

K. Gkiotsalitis. 2021. "A model for modifying the public transport service patterns to account for the imposed COVID-19 capacity." Transportation Research Interdisciplinary Perspectives 9, no. : 100336.

Journal article
Published: 27 February 2021 in Transportmetrica A: Transport Science
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Public transport is one of the most disrupted sectors of the COVID-19 pandemic with reported ridership drops up to 90% in majorly affected countries. As many government authorities strive to partially resume activities, public transport operators are in an urgent need for models that can evaluate the impact of different social distancing policies on operational and passenger-related costs. In this study, we introduce a mixed-integer quadratic programming model for the redesign of public transport services considering the operational, passenger, and revenue loss-related costs by evaluating the effects of different social distancing policies. Our model is applied at the metro network of Washington DC and provides optimal redistribution of vehicles across lines for different social distancing scenarios. This model can be used as a decision support tool by other policymakers and public transport operators that are in need of evaluating the costs related to the implementation of different social distancing policies.

ACS Style

Konstantinos Gkiotsalitis; Oded Cats. Optimal frequency setting of metro services in the age of COVID-19 distancing measures. Transportmetrica A: Transport Science 2021, 1 -21.

AMA Style

Konstantinos Gkiotsalitis, Oded Cats. Optimal frequency setting of metro services in the age of COVID-19 distancing measures. Transportmetrica A: Transport Science. 2021; ():1-21.

Chicago/Turabian Style

Konstantinos Gkiotsalitis; Oded Cats. 2021. "Optimal frequency setting of metro services in the age of COVID-19 distancing measures." Transportmetrica A: Transport Science , no. : 1-21.

Journal article
Published: 10 December 2020 in IEEE Transactions on Intelligent Transportation Systems
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This study proposes an exact model for timetable recovery after disturbances in the context of high-frequency public transport services. The objective of our model is the minimization of the deviation between the actual headway and the respective planned value. The resulting mathematical program for the rescheduling problem is nonlinear and non-smooth; thus, it cannot be solved to optimality. To rectify this, we reformulate the model using slack variables. The reformulated model can be solved to global optimality in real-time with quadratic programming. We apply the model to real data from the red metro line in Washington D.C. in a series of experiments. In our experiments, we investigate how many upstream trips should be rescheduled to respond to a service disturbance. Our findings demonstrate an improvement potential of service regularity of up to 30% if we reschedule the five upstream trips of a disturbed train.

ACS Style

Konstantinos Gkiotsalitis; Oded Cats. Timetable Recovery After Disturbances in Metro Operations: An Exact and Efficient Solution. IEEE Transactions on Intelligent Transportation Systems 2020, PP, 1 -11.

AMA Style

Konstantinos Gkiotsalitis, Oded Cats. Timetable Recovery After Disturbances in Metro Operations: An Exact and Efficient Solution. IEEE Transactions on Intelligent Transportation Systems. 2020; PP (99):1-11.

Chicago/Turabian Style

Konstantinos Gkiotsalitis; Oded Cats. 2020. "Timetable Recovery After Disturbances in Metro Operations: An Exact and Efficient Solution." IEEE Transactions on Intelligent Transportation Systems PP, no. 99: 1-11.

Journal article
Published: 10 December 2020 in Transportation Research Part E: Logistics and Transportation Review
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In this literature review, we systematically review studies on public transit control with a specific focus on at-stop measures. In our synthesis of the relevant literature, we consider three perspectives: (1) the mathematical models of the proposed methodologies; (2) their complexity; (3) their applicability in real-time operations and their advantages and disadvantages considering their practical implications. The reviewed control methods include holding, dynamic dispatching, and stop-skipping. Control methods, that have attracted more attention in recent years due to the advancements in automation and data availability, aim at alleviating the negative effects of service variability because of external disruptions. Following the synthesis of the literature, we propose a research agenda pertaining to the combination of control measures, passenger-oriented decision making, coordinated network control, deployment of electric buses and disturbance management.

ACS Style

K. Gkiotsalitis; O. Cats. At-stop control measures in public transport: Literature review and research agenda. Transportation Research Part E: Logistics and Transportation Review 2020, 145, 102176 .

AMA Style

K. Gkiotsalitis, O. Cats. At-stop control measures in public transport: Literature review and research agenda. Transportation Research Part E: Logistics and Transportation Review. 2020; 145 ():102176.

Chicago/Turabian Style

K. Gkiotsalitis; O. Cats. 2020. "At-stop control measures in public transport: Literature review and research agenda." Transportation Research Part E: Logistics and Transportation Review 145, no. : 102176.

Review
Published: 09 December 2020 in Transport Reviews
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The COVID-19 pandemic crisis has greatly impacted public transport ridership and service provision across the world. As many countries start to navigate their return to normality, new public transport planning requirements are devised. These measures imply a major reduction in service capacity compared to the pre-COVID-19 era. At the time of writing, there is a severe lack of knowledge regarding the potential impact of the pandemic on public transport operations and models that can support the service planning given these new challenges. In this literature review, we systematically review and synthesise the literature on the impacts of COVID on public transport to identify the need to adjust planning measures, and, on the other hand, the existing methods for public transport planning at the strategic, tactical and operational level. We identify intervention measures that can support public transport service providers in planning their services in the post-shutdown phase and their respective modelling development requirements. This can support the transition from the initial ad-hoc planning practices to a more evidence-based decision making.

ACS Style

Konstantinos Gkiotsalitis; Oded Cats. Public transport planning adaption under the COVID-19 pandemic crisis: literature review of research needs and directions. Transport Reviews 2020, 41, 374 -392.

AMA Style

Konstantinos Gkiotsalitis, Oded Cats. Public transport planning adaption under the COVID-19 pandemic crisis: literature review of research needs and directions. Transport Reviews. 2020; 41 (3):374-392.

Chicago/Turabian Style

Konstantinos Gkiotsalitis; Oded Cats. 2020. "Public transport planning adaption under the COVID-19 pandemic crisis: literature review of research needs and directions." Transport Reviews 41, no. 3: 374-392.

Research article
Published: 01 December 2020 in IET Intelligent Transport Systems
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Bus scheduling is a well-known NP-hard problem, and it is addressed with the use of heuristic solution methods or graphical approaches. In this study, the author proposes an improved formulation of the bus scheduling problem that considers the vehicle availability, the vehicle capacity and the allowed headway variability among successive trip dispatches. His formulation expands the classic bus scheduling model formulation by including the aforementioned features. In his study, the bus scheduling problem is understood as the problem of setting the optimal dispatching times for a set of pre-determined daily trips of a particular bus line. His model facilitates the search of solutions that can improve the waiting times of passengers while meeting the operational requirements and avoiding overcrowding. His proposed mathematical program is proved to be non-convex, and it is solved with heuristic solution methods because numerical optimisation approaches cannot guarantee a globally optimal solution. The performance of his approach is tested in a case study using real operational data from bus line 302 in Singapore. A simulation-based evaluation demonstrates potential gains of up to 20% on average passenger waiting times and a major reduction in refused passenger boardings because of overcrowding.

ACS Style

Konstantinos Gkiotsalitis. Bus scheduling considering trip‐varying travel times, vehicle availability and capacity. IET Intelligent Transport Systems 2020, 14, 1594 -1605.

AMA Style

Konstantinos Gkiotsalitis. Bus scheduling considering trip‐varying travel times, vehicle availability and capacity. IET Intelligent Transport Systems. 2020; 14 (12):1594-1605.

Chicago/Turabian Style

Konstantinos Gkiotsalitis. 2020. "Bus scheduling considering trip‐varying travel times, vehicle availability and capacity." IET Intelligent Transport Systems 14, no. 12: 1594-1605.

Journal article
Published: 07 November 2020 in World Electric Vehicle Journal
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Ultrafast charging is developing and will soon be available to electric vehicles (EV). This research focuses on the feasibility of ultrafast charging for EV passenger cars in the Netherlands. We carried out a stated choice experiment with 311 respondents (all EV drivers) and developed mixed logit models based on random utility maximization. In deciding which charging type to choose, this research identified the charging point characteristics, price, proximity to shopping facilities, certainty of charging availability and not having to make a detour as key influential factors for EV drivers. Price changes and not having to make a detour substantially affect users’ choices for the charging types. Contrary to expectations, no significant results were found for urban density, age, technology awareness and importance of sustainability. Finally, the research results show that there is demand for ultrafast charging in the Netherlands even if users have to pay slightly more compared to other forms of charging.

ACS Style

Simone Y. Ten Have; Konstantinos Gkiotsalitis; Karst T. Geurs. Investigating the Future of Ultrafast Charging: A Choice Experiment in the Netherlands. World Electric Vehicle Journal 2020, 11, 70 .

AMA Style

Simone Y. Ten Have, Konstantinos Gkiotsalitis, Karst T. Geurs. Investigating the Future of Ultrafast Charging: A Choice Experiment in the Netherlands. World Electric Vehicle Journal. 2020; 11 (4):70.

Chicago/Turabian Style

Simone Y. Ten Have; Konstantinos Gkiotsalitis; Karst T. Geurs. 2020. "Investigating the Future of Ultrafast Charging: A Choice Experiment in the Netherlands." World Electric Vehicle Journal 11, no. 4: 70.

Journal article
Published: 27 October 2020 in Transportation Research Part C: Emerging Technologies
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This study focuses on single variable optimization approaches which determine the holding time of a vehicle when it is ready to depart from a bus stop. Up to now, single variable optimization methods resort to rule-based control logics to equalize the inter-departure headways or adhere to the target headway values. One of them is the two-headway-based control logic which determines the holding time of a bus based on its headway with its preceding and following bus without addressing other implications, such as overcrowding. To rectify this, we introduce a new model for the single variable bus holding problem that considers the passenger demand and vehicle capacity limits. Then, we reformulate this problem to an easier-to-solve program with the use of slack variables and introduce an analytic solution that can determine the holding time of a vehicle at the respective bus stop. Our analytic solution does not add a computational burden to the two-headway-based control logic and can be applied in real time. The operational benefit of our bus holding approach compared to other analytic solutions that do not consider the vehicle capacity is investigated using actual data from bus line 302 in Singapore.

ACS Style

K. Gkiotsalitis; E.C. van Berkum. An analytic solution for real-time bus holding subject to vehicle capacity limits. Transportation Research Part C: Emerging Technologies 2020, 121, 102815 .

AMA Style

K. Gkiotsalitis, E.C. van Berkum. An analytic solution for real-time bus holding subject to vehicle capacity limits. Transportation Research Part C: Emerging Technologies. 2020; 121 ():102815.

Chicago/Turabian Style

K. Gkiotsalitis; E.C. van Berkum. 2020. "An analytic solution for real-time bus holding subject to vehicle capacity limits." Transportation Research Part C: Emerging Technologies 121, no. : 102815.

Journal article
Published: 21 October 2020 in Accident Analysis & Prevention
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Buses are a form of active transportation and can improve people's well-being. However, their high level of acceleration can make them less attractive to users. Even worse, they can be responsible for severe injuries that require hospitalisation or for the development of fear of falling, particularly experienced by older people. Evidence has shown that, bus acceleration up to 1.0 m/s2 enables passengers to move in a natural way inside the moving vehicle, hence reducing instability and increasing safety. Although operators might be willing to implement such an intervention, they might also be skeptical about its impact on the operation of a service, such as timetabling, travel times, waiting times, etc. The effect of a safety-driven acceleration limit on the operational characteristics of a round trip of a bus service in London is investigated by this study. Data regarding speed, acceleration and journey time were extracted from the engine of a bus and recorded at 2 Hz. Further computations estimated the passenger waiting times and headways between the examined bus and its preceding and following buses. A vehicle movement model was used to test how these operational characteristics would be affected if the acceleration limit of 1.0 m/s2 were to be implemented. The results suggest that the journey time of the proposed accessible service would be 6 min longer than the current service and passenger waiting time would increase by 2 min. One additional bus would be required to serve the same number of passengers. A discussion of the results is provided.

ACS Style

Xenia Karekla; Konstantinos Gkiotsalitis; Nick Tyler. The impact of a passenger-safety-driven acceleration limit on the operation of a bus service. Accident Analysis & Prevention 2020, 148, 105790 .

AMA Style

Xenia Karekla, Konstantinos Gkiotsalitis, Nick Tyler. The impact of a passenger-safety-driven acceleration limit on the operation of a bus service. Accident Analysis & Prevention. 2020; 148 ():105790.

Chicago/Turabian Style

Xenia Karekla; Konstantinos Gkiotsalitis; Nick Tyler. 2020. "The impact of a passenger-safety-driven acceleration limit on the operation of a bus service." Accident Analysis & Prevention 148, no. : 105790.

Articles
Published: 31 July 2020 in Transportmetrica A: Transport Science
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Stop-skipping (also known as expressing) is a typical control strategy in public transit operations with a dual objective: (i) reduce the trip delays, and (ii) improve the travel times of onboard passengers. Dynamic stop-skipping approaches decide about the stop-skipping strategy of each bus trip in isolation, neglecting the effect of the skipped stops on future trips. To rectify this, we introduce a rolling-horizon stop-skipping model that determines the stop-skipping strategies of several trips within a rolling horizon. Then, we model the rolling-horizon stop-skipping problem as an integer nonlinear program, and we prove that it is (at least) an NP-complete decision problem which can be solved to global optimality for small-scale scenarios. Simulation-based tests using real data from bus line 15L in Denver demonstrate a potential performance improvement of 13% when using our rolling horizon stop-skipping approach in the presence of travel time uncertainty.

ACS Style

Konstantinos Gkiotsalitis. Stop-skipping in rolling horizons. Transportmetrica A: Transport Science 2020, 17, 492 -520.

AMA Style

Konstantinos Gkiotsalitis. Stop-skipping in rolling horizons. Transportmetrica A: Transport Science. 2020; 17 (4):492-520.

Chicago/Turabian Style

Konstantinos Gkiotsalitis. 2020. "Stop-skipping in rolling horizons." Transportmetrica A: Transport Science 17, no. 4: 492-520.

Journal article
Published: 27 May 2020 in IEEE Transactions on Intelligent Transportation Systems
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In high-frequency electric bus services, bus operators strive to increase the service regularity by minimizing the deviation between the planned and actual headways. In this pursue, bus operators apply corrective control strategies, such as bus holding(s) at control point stops. This study expands the traditional headway-based, bus holding models to cater for the planned arrival times of electric buses at the respective charging points. To this end, this study models - for the first time - the bus holding problem for electric buses considering the scheduled charging times in the objective function. Additionally, it introduces an analytic solution that can return an optimal holding decision in real-time. Our approach is tested using realistic data from bus line 15 in Amsterdam demonstrating a significant reduction of charging delays with only a marginal increase of the average passenger waiting times when compared to existing holding strategies. Its closed-form expression is suitable for real-time holding control and can be applied to obtain a reliable solution or perform stochastic optimization in the case of travel time uncertainty.

ACS Style

Konstantinos Gkiotsalitis. Bus Holding of Electric Buses With Scheduled Charging Times. IEEE Transactions on Intelligent Transportation Systems 2020, 1 -12.

AMA Style

Konstantinos Gkiotsalitis. Bus Holding of Electric Buses With Scheduled Charging Times. IEEE Transactions on Intelligent Transportation Systems. 2020; (99):1-12.

Chicago/Turabian Style

Konstantinos Gkiotsalitis. 2020. "Bus Holding of Electric Buses With Scheduled Charging Times." IEEE Transactions on Intelligent Transportation Systems , no. 99: 1-12.

Journal article
Published: 01 May 2020 in Journal of Transportation Engineering, Part A: Systems
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This work investigates whether the user-generated data from multiple sources, such as smart cards and social media, can be used to identify main mobility/activity patterns based solely on geo-tagged information. To perform such an analysis, automated models are developed to (1) retrieve user mobility patterns from historical, user-generated data logs, (2) categorize users based on the similarity of their observed mobility patterns, and (3) predict the travel distances of users for participating in future activities. For testing purposes, user-generated data sets from smart card logs and Twitter profiles collected between November 2013 and February 2015 in London are used. User-generated data from 200 smart card and 32 active Twitter users are collected and 6 main clusters are identified based on the mobility/activity pattern similarities of users. Results show that it is possible to integrate data logs from multiple sources to capture the main mobility/activity patterns observed in an area. Results also reveal that the accuracy of the predicted travel distance of one user’s trip can be significantly improved if the user’s previous activities are considered in the prediction process.

ACS Style

Konstantinos Gkiotsalitis; Antony Stathopoulos. Predicting Traveling Distances and Unveiling Mobility and Activity Patterns of Individuals from Multisource Data. Journal of Transportation Engineering, Part A: Systems 2020, 146, 04020025 .

AMA Style

Konstantinos Gkiotsalitis, Antony Stathopoulos. Predicting Traveling Distances and Unveiling Mobility and Activity Patterns of Individuals from Multisource Data. Journal of Transportation Engineering, Part A: Systems. 2020; 146 (5):04020025.

Chicago/Turabian Style

Konstantinos Gkiotsalitis; Antony Stathopoulos. 2020. "Predicting Traveling Distances and Unveiling Mobility and Activity Patterns of Individuals from Multisource Data." Journal of Transportation Engineering, Part A: Systems 146, no. 5: 04020025.

Journal article
Published: 03 April 2020 in Journal of Rail Transport Planning & Management
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In this paper, we study the real-time train assignment problem (RT-TAP) that arises from the unreliable arrival times of freight trains and the last-minute parking requests at railway yards. In the RT-TAP, the reassignment of trains to the yard is triggered every time a train arrives at the railway yard and needs to be assigned (event-based optimization). After introducing a problem formulation for the RT-TAP problem, we prove that RT-TAP is NP-Hard. In particular, the RT-TAP is modeled as a mixed integer program that strives to minimize the total weighted delay of trains. Because of its computational complexity and the time-critical nature of this problem, we introduce two real-time solution methods: (a) a problem-specific genetic algorithm (GA), (b) and a first-scheduled first-served (FSFS) heuristic. In small instances, we show that the GA returns a globally optimal solution which is identical to the solution of exact optimization methods. In larger problem instances, the heuristic approaches of FSFS and GA are tested at the Waalhaven Zuid railway yard in the Netherlands using two months of operational data. In the experimental results, the GA solutions reduce the average delays by more than 4 min compared to the solutions of the FSFS heuristic.

ACS Style

B.B.W. Schasfoort; K. Gkiotsalitis; O.A.L. Eikenbroek; E.C. van Berkum. A dynamic model for real-time track assignment at railway yards. Journal of Rail Transport Planning & Management 2020, 14, 100198 .

AMA Style

B.B.W. Schasfoort, K. Gkiotsalitis, O.A.L. Eikenbroek, E.C. van Berkum. A dynamic model for real-time track assignment at railway yards. Journal of Rail Transport Planning & Management. 2020; 14 ():100198.

Chicago/Turabian Style

B.B.W. Schasfoort; K. Gkiotsalitis; O.A.L. Eikenbroek; E.C. van Berkum. 2020. "A dynamic model for real-time track assignment at railway yards." Journal of Rail Transport Planning & Management 14, no. : 100198.

Journal article
Published: 18 February 2020 in Applied Mathematical Modelling
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We model the problem of dispatching time control in rolling horizons following a periodic optimization approach reactionary to travel time and passenger demand disturbances. This model provides more flexibility to transport planners allowing them to adjust the bus schedules during the daily operations. We prove that our periodic optimization model is a convex quadratic program, guaranteeing the global optimality of its solution. To reduce the computational burden, we introduce an iterative algorithm that uses gradient approximations to obtain an approximate dispatching solution. The proposed solution method is found to be significantly faster than exact optimization approaches for quadratic programming and maintains an (almost) negligible optimality gap in realistic bus operation scenarios. Finally, we show that our periodic optimization method outperforms myopic methods that adjust the dispatching time of each bus trip in isolation using operational data from bus line 302 in Singapore.

ACS Style

K. Gkiotsalitis. A model for the periodic optimization of bus dispatching times. Applied Mathematical Modelling 2020, 82, 785 -801.

AMA Style

K. Gkiotsalitis. A model for the periodic optimization of bus dispatching times. Applied Mathematical Modelling. 2020; 82 ():785-801.

Chicago/Turabian Style

K. Gkiotsalitis. 2020. "A model for the periodic optimization of bus dispatching times." Applied Mathematical Modelling 82, no. : 785-801.

Preprint content
Published: 18 December 2019
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In the past years, there has been an emerging number of studies on estimating the passenger demand in urban environments based on social media and cellular data. However, the study of the travel behavior at the individual level and the relation between social media activity and the activity/mobility patterns of users has received limited attention. To rectify this, this study examines Twitter data for unveiling the relations between geo-tagged Tweets and Twitter user sentiments, and the respective activity types performed in the real-world. In this work we try to find common patterns between users' Twitter activity and their actual mobility/activity patterns with the aim to provide some generalizations that can help to understand and model the travel behavior of users. This is achieved with the development of educated rules and probabilistic models that can predict the mobility transfers of users between different activities based solely on social media data. The validity of our generalizations is validated with the use of 4-month Twitter data from London. Only active Twitter users have been selected to study in deep the relations between social media activities/sentiments and the activity types performed in the real-world. Although our generalizations are case study-specific, they demonstrate that it is possible to extract the activity and mobility behavior of users with the use of social media and offer a first step in this direction.

ACS Style

Konstantinos Gkiotsalitis. Investigating the relation between social media activities and the mobility and activity types of users. 2019, 1 .

AMA Style

Konstantinos Gkiotsalitis. Investigating the relation between social media activities and the mobility and activity types of users. . 2019; ():1.

Chicago/Turabian Style

Konstantinos Gkiotsalitis. 2019. "Investigating the relation between social media activities and the mobility and activity types of users." , no. : 1.

Journal article
Published: 26 November 2019 in Transportation Research Part C: Emerging Technologies
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In this work, we adapt the rolling-horizon approach of Eberlein et al. (2001) for adjusting the dispatching times of buses at each rolling horizon. The industry practice is to adjust the dispatching time of a bus once it departs from the first stop while considering that future trips will operate as planned. In contrast, a rolling-horizon approach adjusts simultaneously the dispatching times of all trips that operate during a pre-determined time interval resulting in a coordinated effort to maintain the target headways. Due to the increased number of dispatching time decisions, this coordinated effort increases the computational burden. To reduce the computational cost, we introduce a nonlinear program and we propose a novel reformulation that limits the recursive relations of the optimization problem. Our program is proved to be convex and can be solved to global optimality under a limited computational cost. In addition, it outperforms myopic methods that adjust the dispatching time of each bus trip in isolation. The sensitivity of our method to travel time and passenger demand fluctuations is investigated on a simulation scenario of bus line 15L in Denver.

ACS Style

K. Gkiotsalitis; E.C. van Berkum. An exact method for the bus dispatching problem in rolling horizons. Transportation Research Part C: Emerging Technologies 2019, 110, 143 -165.

AMA Style

K. Gkiotsalitis, E.C. van Berkum. An exact method for the bus dispatching problem in rolling horizons. Transportation Research Part C: Emerging Technologies. 2019; 110 ():143-165.

Chicago/Turabian Style

K. Gkiotsalitis; E.C. van Berkum. 2019. "An exact method for the bus dispatching problem in rolling horizons." Transportation Research Part C: Emerging Technologies 110, no. : 143-165.

Articles
Published: 29 October 2019 in Journal of Intelligent Transportation Systems
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Given the unstable nature of the bus operations, the regularity of the bus services cannot be maintained throughout the day. Especially in densely populated areas, the inherent variability of the trip travel times affects the regularity of the daily services since the arrival times of several trips at stops might oscillate significantly from their expected values. Because of the high level of uncertainty, this work proposes a periodic rescheduling of the dispatching times of the daily bus trips to adjust continuously to the operational changes. A key differentiator from previous works is that a periodic rescheduling does not focus only on the running buses, but also reschedules the dispatching times of all remaining daily trips while considering operational constraints related to layover times and capacity limits. Typical scheduling problems (such as a bus scheduling problem) are NP-hard because of the discrete nature of the decision variables. Hence, the computational burden prohibits their solution with analytical methods. Catering for capacity limits increases further the complexity of our problem because it results in a non-smooth objective function which is not differentiable at every point of its domain. For this reason, this work proposes a sequential hill climbing method to search the solution space more efficiently and reschedule the dispatching times of trips in near real time. This approach is tested using real-time data from bus line 15 L in Denver, USA. Critical issues, such as to what extent can the periodic dispatching time rescheduling improve the regularity of daily operations, are investigated.

ACS Style

Konstantinos Gkiotsalitis. Bus rescheduling in rolling horizons for regularity-based services. Journal of Intelligent Transportation Systems 2019, 25, 356 -375.

AMA Style

Konstantinos Gkiotsalitis. Bus rescheduling in rolling horizons for regularity-based services. Journal of Intelligent Transportation Systems. 2019; 25 (4):356-375.

Chicago/Turabian Style

Konstantinos Gkiotsalitis. 2019. "Bus rescheduling in rolling horizons for regularity-based services." Journal of Intelligent Transportation Systems 25, no. 4: 356-375.