Konstantinos N. Androutsopoulos

A heuristic algorithm for solving hazardous materials distribution problems

A type of decision of major importance that directly affects the performance of a distribution system is the routing and scheduling of delivery trucks. The determination of hazardous materials distribution routes can be defined as a bi-objective vehicle routing problem with time windows since risk minimization accompanies the cost minimization in the objective function. The objective of this paper is to present a new heuristic algorithm for solving the bi-objective vehicle routing and scheduling problem. The proposed algorithm has been applied to several benchmark problems. The results of these applications seem to be quite encouraging. Furthermore, the proposed algorithm has been integrated within a GIS based decision support system for hazardous materials logistics operations providing valid preliminary results on a set of case studies.

Algorithms for Itinerary Planning in Multimodal Transportation Networks

The itinerary planning problem in an urban public transport system constitutes a common routing and scheduling decision faced by travelers. The objective of this paper is to present a new formulation and an algorithm for solving the itinerary planning problem, i.e., determination of the itinerary that lexicographically optimizes a set of criteria (i.e., total travel time, number of transfers, and total walking and waiting time) while departing from the origin and arriving at the destination within specified time windows. Based on the proposed formulation, the itinerary planning problem is expressed as a shortest path problem in a multimodal time-schedule network with time windows and time-dependent travel times. A dynamic programming-based algorithm has been developed for the solution of the emerging problem. The special case of the problem involving a mandatory visit at an intermediate stop within a given time window is formulated as two nested itinerary planning problems which are solved by the aforementioned algorithm. The proposed algorithm has been integrated in a Web-based journey planning system, whereas its performance has been assessed by solving real-life itinerary planning problems defined on the Athens urban public transport network, providing fast and accurate solutions.

A Real Time Decision Support System for Roadway Network Incident Response Logistics

Incident-related congestion is a serious problem of great concern for most metropolitan traffic management authorities. The high economic and social impact associated with the incident-related congestion has prompted Traffic Management Agencies world-wide to develop incident management systems (IMS). Incident response logistics (IRL) encompass all actions needed for the effective deployment of incident response resources and constitute an essential component of any IMS. The incident management decision making environment suggests that decision support systems (DSSs) can be used in order to improve the quality of the decisions and expedite the decision making process of the IRL. The objective of this paper is to develop a DSS for supporting real-time decisions related to IRL. The development of the proposed DSS is based on an extensive user-requirements survey in six European countries and integrates mathematical models, rules and algorithms in a user friendly environment in order to minimise incident response time. The proposed DSS provides the following functionalities: (i) districting, (ii) dispatching of response units (RUs), (iii) routing of the RUs, and (iv) on-scene management and it has been demonstrated successfully under real life conditions and accepted as a useful decision making tool by its users.

Solving the multi-criteria time-dependent routing and scheduling problem in a multimodal fixed scheduled network

Multi-criteria routing and scheduling in a multimodal fixed scheduled network with time-dependent travel times involves the determination of the non-dominated itineraries (i.e., paths enhanced with scheduled departures) under the following constraints: (i) visiting a given set of intermediate stops in a specified sequence, and (ii) strict time windows on the origin, the destination and the intermediate stops. The objective of this paper is to present the formulation and algorithmic solution for the multi-criteria itinerary planning problem that takes into account the aforementioned features. The algorithmic approach proposed is based on the decomposition of the problem to a sequence of elementary itinerary sub-problems, solved by a dynamic programming algorithm. The computational performance of the algorithms on a set of large scale test problems indicates non-prohibitive time requirements and encourages its integration into travel planning decision support systems.

Design and Assessment of an Online Passenger Information System for Integrated Multimodal Trip Planning

This paper presents the design and evaluation of an online passenger information system for delivering personalized multimodal trip planning services through the integration of wireless and Web-based communication technologies. The goal of the system is to provide real-time travel information throughout the entire life cycle of an interurban trip. Before the full-scale deployment of this type of system, it is essential to assess its impact on the involved stakeholders through a pilot application. The proposed system (ENOSIS) has been implemented and evaluated for supporting travel decisions in Greece. An evaluation framework for assessing the impacts of the ENOSIS system is proposed, and the evaluation results of the ENOSIS pilot application are also reported. The evaluation results provide significant evidence of the technical and operational efficiency of the ENOSIS services, while it is shown that the proposed system is cost effective.

Integrated Passenger Information System for Multimodal Trip Planning

The integration of wireless and web-based communication technologies in advanced public transport information systems has led to the provision of passenger information services directly to the users. Most of the existing systems provide alternative travel plans either for urban or for single-mode interurban trips. The objective of this paper is to present an online passenger information system for delivering personalized trip-planning services for interurban multimodal trips, including plans for any constituent urban transfer. The proposed system accommodates the provision of critical real-time travel information (e.g., delay or cancelation of flights) to the user throughout the entire life cycle of an interurban trip. The major features of the system are the following: (a) determination of optimum itineraries in a multimodal public transportation network, (b) online updates of the departure times throughout the entire life cycle of the trip, and (c) dissemination of travel information through several communication channels. The proposed system supports two major trip-planning decisions: (a) itinerary planning for an urban trip through the local public transport network, and (b) combined urban and interurban trip planning. The focus of the paper is on the presentation of the design and implementation of the proposed system and its application for supporting trip-planning decisions in Greece. An evaluation of the system has indicated that it is user-friendly, is cost-effective, and meets travelers’ requirements.

Solving the k-shortest path problem with time windows in a time varying network

The k-shortest path problem in a network with time dependent cost attributes arises in many transportation decisions including hazardous materials routing and urban trip planning. The present paper proposes a label setting algorithm for solving this problem given that departure and arrival are constrained within specified time windows.

A bi-objective time-dependent vehicle routing and scheduling problem for hazardous materials distribution

Planning hazardous materials distribution routes for servicing a given set of orders within specified time windows is a problem frequently surfacing in a city logistics environment which is characterized by dynamic travel times. The hazardous materials distribution problem involves the determination of the sequence of deliveries and the corresponding paths assigned to each truck. This paper presents the formulation of the hazardous materials distribution problem as a bi-objective time-dependent vehicle routing problem with time windows. The paper presents the mathematical formulation of the problem as an integer network flow model with multiple objectives. The weighted-sum method is applied decomposing the bi-objective vehicle routing and scheduling problem to a series of single-objective instances of the problem, where the objective function is expressed by the weighted sum of the criteria under consideration. A route-building heuristic algorithm is presented for addressing each of the constituent single-objective problems, where stops are inserted iteratively in the front part of the unfinished route. A label-setting algorithm is integrated in the heuristic algorithm for solving the time-dependent shortest path problem with multiple intermediate stops arising after the insertion of any stop in the route. The proposed solution approach has been applied to a set of solvable test problems to assess the accuracy of the heuristic solutions. The results indicate a tolerable deviation of the heuristic solutions from the actual non-dominated solutions. In addition, the proposed algorithm was applied to a set of test problems resembling real-life problem cases. The average computational time needed for solving this type of test problems is not prohibitive.

Increasing airport capacity utilisation through optimum slot scheduling: review of current developments and identification of future needs

Most of the busiest airports worldwide experience serious congestion and delay problems which call for some immediate capacity and demand management action. Solutions aiming to manage congestion through better slot scheduling have lately received a great deal of consideration due to their potential for delivering quick and substantial capacity utilisation improvements. A slot scheduling approach brings promises to cope better with congestion problems in the short to medium run and in a more sustainable way based on existing resources. This paper aims to provide a critical review of current research in declared capacity modelling and strategic slot scheduling. Furthermore, it goes beyond the critical review of current research developments by identifying future research issues and gaps and developing concrete directions towards modelling and solving advanced single airport and network-based slot scheduling problems. Our research findings suggest that the next generation of slot scheduling models should explore variations of currently used objectives (e.g., alternative expressions of schedule delay) and most importantly enrich them with fairness and equity, resource utilisation and environmental considerations. Future modelling efforts should also aim to further investigate airlines’ utility of alternative slot allocation outcomes, including various acceptability measures and levels of tolerance against schedule displacements. Last but not least, future research should intensively focus on the development and validation of computationally viable and robust slot scheduling models being able to capture the complexity, dynamic nature and weather-induced uncertainty of airport operations, along with hybrid solution approaches being able to deal with the size and complexity of slot allocation at network level.

An operational centre for managing major chemical industrial accidents

The most important characteristic of major chemical accidents, from a societal perspective, is their tendency to produce off-site effects. The extent and severity of the accident may significantly affect the population and the environment of the adjacent areas. Following an accident event, effort should be made to limit such effects. Management decisions should be based on rational and quantitative information based on the site specific circumstances and the possible consequences. To produce such information we have developed an operational centre for managing large-scale industrial accidents. Its architecture involves an integrated framework of geographical information system (GIS) and RDBMS technology systems equipped with interactive communication capabilities. The operational centre was developed for Windows 98 platforms, for the region of Thriasion Pedion of West Attica, where the concentration of industrial activity and storage of toxic chemical is immense within areas of high population density. An appropriate case study is given in order to illuminate the use and necessity of the operational centre.