Christina Iliopoulou

Last Name

Iliopoulou

First Name

Christina

ORCID

0000-0002-9888-1947

Show all metadata

Search Results

Publications 1 - 10 of 31

Resilience-oriented design for public transport networks
Iliopoulou, Christina; Makridis, Michail; Kouvelas, Anastasios (2023)
hEART 2023: 11th Symposium of the European Association for Research in Transportation
Public transport systems are typically designed based on estimated passenger demand and sup-ply patterns, yet may often be called to operate under vastly different operational settings. To systematically design resilient transit systems, it is necessary to “weave” resilience-oriented thinking into the established public transport network design process, moving from an abstract concept to an implementable methodology. This study aims to effectively and efficiently design resilient public transport networks through the integration of Reinforcement Learning (RL), Local Search operators and Particle Swarm Optimization. We present a redundancy indicator and integrate it within a hybrid RL-enhanced metaheuristic solution framework to design more resilient route structures. We apply the proposed Memetic algorithm to an established benchmark from the literature and validate the proposed approach under a series of random and targeted attacks, simulating link disruptions. Results demonstrate that resilience can be enhanced through redundancy without adversely impacting average travel times.
Identifying spatio-temporal patterns of bus bunching in urban networks
Iliopoulou, Christina; Milioti, Christina P.; Vlahogianni, Eleni I.; et al. (2020)
Journal of Intelligent Transportation Systems
The objective of this paper is to identify hot spots of bus bunching events at the network level, both in time and space, using Automatic Vehicle Location (AVL) data from the Athens (Greece) Public Transportation System. A two-step spatio-temporal clustering analysis is employed for identifying localized hot spots in space and time and for refining detected hot spots, based on the nature of bus bunching events. First, the Spatio-Temporal Density Based Scanning Algorithm with Noise (ST-DBSCAN) is applied to distinguish bunching patterns at the network level and subsequently a k++means algorithm is employed to distinguish different types of bunching clusters. Results offer insights on specific time periods and route segments, where bus bunching events are more likely to occur and, also, on how bus bunching clusters change over time. Further, headway deviation analysis reveals the differences in the characteristics of the various bunching event types per line, showing that routes running on shared corridors experience more issues while underlying causes may vary per line. Collectively, results can help guide practice toward more flexible solutions and control strategies. Indeed, depending on the type of spatio-temporal patterns detected, appropriate improvements in service planning and real-time control strategies may be identified in order to mitigate their negative effects and improve quality of service. In light of emerging electric public transport systems, the proposed framework can be also used to determine preventive strategies and improve reliability in affected stops prior to the deployment of charging infrastructure.
Route planning for a seaplane service: The case of the Greek Islands
Iliopoulou, Christina; Kepaptsoglou, Konstantinos; Karlaftis, Matthew G. (2015)
Computers & Operations Research
Seaplanes offer a time and cost-efficient service for supporting transportation needs in island chains. This paper investigates the design of a seaplane network connecting the Greek islands with the mainland, a service currently accommodated by ferries. Design of seaplane routes is modeled as a multi-objective capacitated vehicle routing problem with simultaneous pickups and deliveries and route length deadlines. A genetic algorithm coupled with a hybrid process is used to solve the model. Results show that a network of 11 routes with maximum flight duration of 5 h can adequately cover estimated daily transportation needs between the Greek mainland and the islands. Further, realistic increases in seaplane capacity and/or cruising speed will have only a moderate impact on reducing the number of required routes.
ITS Technologies for Decision Making during Evacuation Operations: A Review
Iliopoulou, Christina; Konstantinidou, Maria A.; Kepaptsoglou, Konstantinos L.; et al. (2020)
Journal of Transportation Engineering, Part A: Systems
As natural and human-induced disasters have increased in recent years in number, magnitude, and impacts, the frequency of evacuation orders is expected to be accordingly raised in the future. Practice has shown, however, that many times, the respective operations face impediments, thus indicating the need for efficient tools to facilitate them. Intelligent transportation systems (ITS) have been recognized as a promising strategy in this direction. In this context, this study presents a comprehensive overview of current practices and research efforts regarding the use of ITS in real-time evacuation operations; the scope is to synthesize and critically discuss the state of the practice and state of the art on ITS-assisted decision making in evacuation management. Emphasis is placed on the modeling tools required for adequate representation of real-time evacuation conditions and on the role of emerging technologies in this field. Research findings are analyzed, challenges faced by transportation authorities are identified, and promising future directions are proposed. The paper concludes with a sociobehavioral analysis of the role of information provision in disaster settings, discussing its influence and the possible implications and complications arising, as well as reviewing relevant research studies from the evacuation literature.
A Variable Neighbourhood Search-Based Algorithm for the Transit Route Network Design Problem
Iliopoulou, Christina; Tassopoulos, Ioannis; Beligiannis, Grigorios (2022)
Applied Sciences
The transit route network design problem (TRNDP) has long attracted research attention, with many metaheuristic approaches proposed for its solution. So far, and despite the promising performance of Variable Neighbourhood Search (VNS) variants for vehicle routing problems, the performance of the algorithm on the TRNDP remains unexplored. In this context, this study develops a VNS-based algorithm for the problem at hand. The performance of the algorithm is tested using benchmark networks used in bus transit network design and compared with some of the most recent and efficient methods from the literature. Results show that the algorithm yields superior results over existing implementations in short computational times.
Energy supply security for the Aegean islands: A routing model with risk and environmental considerations
Iliopoulou, Christina; Kepaptsoglou, Konstantinos; Schinas, Orestis (2018)
Energy Policy
Energy security is important for islands not connected to mainland electricity grids. The Aegean archipelago comprises scattered islands, whose electricity supply relies on oil-based thermal power plants. These islands attract large numbers of tourists, while the archipelago is an environmentally sensitive area. Efficient maritime transportation of crude oil is critical for maintaining adequate power supply in the Aegean islands, especially during tourist seasons. Tanker closed-sea shipping operations in the Aegean Sea raise considerations on carbon footprint impacts. Also, despite potential impacts to local economies and the environment, the case of a maritime accident leading to an oil spill is largely overlooked. We investigate the possible integration of environmental and accident related objectives, in the decision-making process of planning an efficient oil maritime transportation service for the Aegean archipelago. We showcase a risk mitigation strategy for oil transport route planning considering spill-related impacts to local, tourism dependent economies under a more socially and environmentally conscious policy framework. We model the problem as a multi-objective capacitated vehicle routing problem and solve it using an alternating objective genetic algorithm. Results show that certain routes are considered optimal for both objectives, while risk reduction may be achieved at small operational cost increase.
Battery-Assisted Trolleybus Network Design: Model and Application
Stavropoulou, Eirini; Iliopoulou, Christina; Kepaptsoglou, Konstantinos (2022)
Journal of Transportation Engineering, Part A: Systems
Battery-assisted trolleybuses (BATs) are among the options to be considered for electrifying bus fleets in cities, with establishedtrolleybus catenary networks. BATs charge on the move using existing trolleybus catenaries and can extend their routes using onboardbatteries. As such, in cases where thermal bus lines overlap to some extent with a trolleybus catenary network, these may be replacedby BATs; such a case has the advantage of avoiding either opportunity charging facilities or the use of (heavy) electric buses operatingunder a depot-charging scheme. Aiming at exploiting these operational advantages, this paper proposes a transit route network electrificationproblem dealing with the optimal selection of existing bus lines to be operated by BATs. The proposed model was applied to a real-world casestudy in Athens, Greece, with results showing that design objective prioritization largely affects the degree of electrification attained.
Demonstrative Case of a Pedestrian Network Design Model Considering Effects on Motorized Traffic
Iliopoulou, Christina; Tseliou, Maria; Kepaptsoglou, Konstantinos; et al. (2020)
Transportation Research Record
The transformation of urban roadways into pedestrian streets is a popular measure for reshaping city parts and enhancing their livability. Nevertheless, pedestrianization schemes are expected to have some impact on the performance of the neighboring road network, especially if these are established ad-hoc or solely based on non-transport criteria. This study introduces a methodological tool for supporting decisions on implementing pedestrianization schemes in urban networks. A bi-level network design model variant is developed for that purpose, whose design objective is to maximize the extent of pedestrian streets in an urban network, while maintaining acceptable impacts to the performance of the road network. Alternative decisions on pedestrianization are considered for each network segment; these include partial (one-directional) or complete (bi-directional) pedestrianization under physical and operational criteria and constraints. The model is applied for a mid-sized urban network in Greece and solved using a genetic algorithm. Results show that the pedestrianization of almost 7% of the road network in relation to length leads to a 40% increase in total network travel time, while a higher ratio of complete versus partial pedestrianization is more advantageous. Outcomes also reveal that that rigid design guidelines should be examined in a case-by-case approach, as superior results may be attained if some constraints, such as those related to the overall street width, are relaxed. Reasonably, policy priorities significantly impact generated solutions and are expected to play a decisive role in the design of pedestrianization schemes.
Solar-powered bus route: introducing renewable energy into a university campus transport system
Ioannidis, Romanos; Iliopoulou, Theano; Iliopoulou, Christina; et al. (2019)
Advances in Geosciences
We investigate the application of a solar-powered bus route to a small-scale transportation system, as such of a university campus. In particular, we explore the prospect of replacing conventional fossil fuel buses by electric buses powered by solar energy and electricity provided by the central grid. To this end, we employ GIS mapping technology to estimate the solar radiation at the university campus and, accordingly, we investigate three different scenarios for harnessing the available solar power: (1) solar panels installed on the roof of bus stop shelters, (2) solar panels installed at an unused open space in the university, and (3) solar roads, i.e. roads constructed by photovoltaic (PV) materials. For each of the three scenarios, we investigate the optimal technical configuration, the resulting energy generation, as well as the capital cost for application in the case of NTUA campus in Athens (Greece). The preliminary feasibility analysis showcases that all three scenarios contribute to satisfying transportation demand, proportionately to their size, with scenario (2) presenting the lowest capital cost in relation to energy generation. Therefore, we further explore this scenario by simulating its daily operation including the actions of buying and selling energy to the central grid, when there is energy deficit or surplus, respectively. A sensitivity analysis is carried out in order to ascertain the optimal size of the solar panel installation in relation to profit and reliability. Overall, results indicate that, albeit the high capital costs, solar-powered transportation schemes present a viable alternative for replacing conventional buses at the studied location, especially considering conventional PV panels. We note that present results heavily depend on the choice of capacity factors of PV materials, which differ among technologies. Yet, as capacity factors of PV panels are currently increasing, the studied schemes might be more promising in the future.
Metaheuristics for the transit route network design problem: a review and comparative analysis
Iliopoulou, Christina; Kepaptsoglou, Konstantinos; Vlahogianni, Eleni (2019)
Public Transport
This paper critically reviews applications of metaheuristics for solving the Transit Route Network Design Problem (TRNDP). A structured review is offered and prominent metaheuristics for tackling the TRNDP are evaluated, according to a benchmark network. The review findings yield a unified implementation framework, which contains common algorithmic components and different solution representations and methods, which are considered important for obtaining solutions of good quality. The paper concludes with identified gaps in research and opportunities for future research on the application of metaheuristic algorithms for solving the TRNDP.

Publications 1 - 10 of 31

Christina Iliopoulou

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results