Multimodal urban mobility and multilayer transport networks

Transportation networks, from bicycle paths to buses and railways, are the backbone of urban mobility. In large metropolitan areas, the integration of different transport modes has become crucial to guarantee the fast and sustainable flow of people. Using a network science approach, multimodal transport systems can be described as multilayer networks, where the networks associated to different transport modes are not considered in isolation, but as a set of interconnected layers. Despite the importance of multimodality in modern cities, a unified view of the topic is currently missing. Here, we provide a comprehensive overview of the emerging research areas of multilayer transport networks and multimodal urban mobility, focusing on contributions from the interdisciplinary fields of complex systems, urban data science, and science of cities. First, we present an introduction to the mathematical framework of multilayer networks. We apply it to survey models of multimodal infrastructures, as well as measures used for quantifying multimodality, and related empirical findings. We review modelling approaches and observational evidence in multimodal mobility and public transport system dynamics, focusing on integrated real-world mobility patterns, where individuals navigate urban systems using different transport modes. We then provide a survey of freely available datasets on multimodal infrastructure and mobility, and a list of open source tools for their analyses. Finally, we conclude with an outlook on open research questions and promising directions for future research.Comment: 31 pages, 4 figure

Assessing the Impact of Multi-variate Steering-rate Vehicle Control on Driver Performance in a Simulation Framework

When a driver turns a steering-wheel, he or she normally expects the vehicle\u27s steering system to communicate an equivalent amount of signal to the road-wheels. This relationship is linear and occurs regardless of the steering-wheel\u27s position within its rotational travel. The linear steering paradigm in passenger vehicles has gone largely unchanged since mass production of passenger vehicles began in 1901. However, as more electronically-controlled steering systems appear in conjunction with development of autonomous steering functions in vehicles, an opportunity to advance the existing steering paradigms arises. The following framework takes a human-factors approach toward examining and evaluating alternative steering systems by using Modeling and Simulation methods to track and score human performance. Present conventional steering systems apply a linear relationship between the steering-wheel and the road wheels of a vehicle. The rotational travel of the steering-wheel is 900° and requires two-and-a-half revolutions to travel from end-stop to opposite end-stop. The experimental steering system modeled and employed in this study applies a dynamic curve response to the steering input within a shorter, 225° rotational travel. Accommodation variances, based on vehicle speed and steering-wheel rotational position and acceleration, moderate the apparent steering input to augment a more-practical, effective steering rate. This novel model follows a paradigm supporting the full range of steering-wheel actuation without necessitating hand repositioning or the removal of the driver\u27s hands from the steering-wheel during steering maneuvers. In order to study human performance disparities between novel and conventional steering models, a custom simulator was constructed and programmed to render representative models in a test scenario. Twenty-seven males and twenty-seven females, ranging from the ages of eighteen to sixty-five were tested and scored using the driving simulator that presented two successive driving test vignettes: One vignette using conventional 900° steering with linear response and the other employing the augmented 225° multivariate, non-linear steering. The results from simulator testing suggest that both males and females perform better with the novel system, supporting the hypothesis that drivers of either gender perform better with a system augmented with 225° multivariate, non-linear steering than with a conventional steering system. Further analysis of the simulated-driving scores indicates performance parity between male and female participants, supporting the hypothesis positing no significant difference in driver performance between male and female drivers using the augmented steering system. Finally, composite data from written questionnaires support the hypothesis that drivers will prefer driving the augmented system over conventional steering. These collective findings support justification for testing and refining novel steering systems using Modeling and Simulation methods. As a product of this particular study, a tested and open-sourced simulation framework now exists such that researchers and automotive designers can develop, as well as evaluate their own steering-oriented products within a valid human-factors construct. The open-source nature of this framework implies a commonality by which otherwisedisparate research and development work can be associated. Extending this framework beyond basic investigation to reach applications requiring morespecialized parameters may even impact drivers having special needs. For example, steeringsystem functional characteristics could be comparatively optimized to accommodate individuals afflicted with upper-body deficits or limited use of either or both arms. Moreover, the combined human-factors and open-source approaches distinguish the products of this research as a common and extensible platform by which purposeful automotive-industry improvements can be realized—contrasted with arbitrary improvements that might be brought about predominantly to showcase technological advancements

Estimation of factors of penalty time in the function of generalized cost in Bucaramanga and its metropolitan area

The travel time is a natural measure of the operation of a route or a transport system, where one of the main objectives is to transport people, cargo, goods, and services. The measure or factor by which people measure subjectively the effectiveness of the road or transportation system is the time it takes to travel, some elements such as the landscape, the environment, the availability of seats and others are elements responsible for providing a sense of comfort and help the user perception regarding the trip better, simpler routes also provide comfort feeling trip by the passenger, but its main goal is to reach as quickly as possible to your destiny.When a person takes a trip, the factor that is reviewed is the travel time, but also to make the programming of public transport routes should be incorporated to travel qualitative attributes such as comfort, safety, and prestige of the transport mode. That is the time value is usually higher in situations of congestion or where the traveler is not comfortable, so the author in his book Ortúzar Transportation Demand Models suggests that the cost of travel time The travel time is a natural measure of the operation of a route or a transport system, where one of the main objectives is to transport people, cargo, goods, and services. The measure or factor by which people measure subjectively the effectiveness of the road or transportation system is the time it takes to travel, some elements such as the landscape, the environment, the availability of seats and others are elements responsible for providing a sense of comfort and help the user perception regarding the trip better, simpler routes also provide comfort feeling trip by the passenger, but its main goal is to reach as quickly as possible to your destiny.When a person takes a trip, the factor that is reviewed is the travel time, but also to make the programming of public transport routes should be incorporated to travel qualitative attributes such as comfort, safety, and prestige of the transport mode. That is the time value is usually higher in situations of congestion or where the traveler is not comfortable, so the author in his book Ortúzar Transportation Demand Models suggests that the cost of travel time should be measured by travel segment. Some of the times that are considered are: the walking time to the whereabouts, the waiting time at the bus stop and the travel time on the bus (in this aspect should be considered if the bus is idle or not, this in to review the accommodations on the trip)El tiempo de viaje es una medida natural de la operatividad de una vía o de cualquier  sistema de transporte, en especial en sistemas masivos exclusivos tipo BRT (Bus Rapid Transit) o colectivo, donde uno de los principales objetivos del sistema de transporte público es el de movilizar personas, cargas, bienes y servicios. La medida o factor por el cual las personas miden subjetivamente la efectividad de la vía o del sistema de transporte, es el tiempo que les toma realizar el viaje, algunos elementos tales como el paisaje, el ambiente, la disponibilidad de asientos entre otros son elementos encargados de proporcionar una sensación de confort y ayudan a que la percepción del usuario con respecto al viaje sea mejor; las rutas simples también aportan sensación de confort al viaje realizado por el pasajero, pero su principal objetivo es llegar en el menor tiempo posible a su destino.   Cuando una persona realiza un viaje, el factor que más se revisa es el tiempo de viaje, pero también al realizar la programación de rutas de transporte público se debe incorporar atributos cualitativos al viaje tales como confort, seguridad y prestigio del modo de transporte. Es decir el valor del tiempo suele ser mayor en situaciones de congestión o donde el viajero no se encuentra confortable, Ortúzar sugiere que el costo del tiempo de viaje debe ser medido por segmento de viaje. Algunos de los tiempos que se consideran son: El tiempo de caminata hasta el paradero, el tiempo de espera en el paradero, el tiempo de viaje en el bus (En este aspecto se debe considerar si el bus está desocupado o no, esto con el fin de revisar el confort y la comodidad en el viaje)

Parallel computation of large-scale network equilibria and variational inequalities.

Equilibrium of a network is obtained when each user who competes to optimize his utility can not improve his utility any further. Equilibrium problems governed by distinct equilibrium concepts can be formulated in one general framework--that of variational inequalities. The synthesis of variational inequalities and networks induces the creation of highly efficient algorithms which are especially suited for the large-scale equilibrium problems. Motivated by the recent technological advances in parallel computing architectures, parallel algorithms of large-scale equilibrium problems were developed using the theory of variational inequalities. In the case where the feasible constraint set of a network equilibrium problem can be expressed as a Cartesian product of subsets, the application of variational inequality decomposition algorithms for the parallel computation becomes possible. A new spatial price equilibrium model, which is not based on the path flows, but, rather, on the link flows to allow the decomposition by time periods, was developed and used as a prototype of large-scale network equilibrium problems. The variational inequality formulations were decomposed first by commodities, then by time periods, and, subsequently, by markets. The coarse grain parallel architectures used were the IBM 3090-600E and the IBM 3090-600J at the Cornell Theory Center with six processors each. The maximum speed-ups obtained were 1.93 for two processors, 3.74 for four processors, and 5.15 for six processors. The market subproblems were further decomposed by links, resulting in a fine grain parallel implementation. The Thinking Machine\u27s Connection Machine, CM-2, with 32,768 processors was used for the numerical experimentation. The fine grain parallel algorithm solved input/output matrix problems more than 20 times faster, when compared to the results on the IBM 3090-600J. It is expected that further enhancements to parallel languages and parallel architectures will make even more efficient implementations realizable, and that parallel computing and the theory of variational inequalities can be successfully applied to solve more efficiently other large-scale problems with an underlying network structure, such as traffic equilibrium problems, general economic equilibrium problems, and financial equilibrium problems

Doctor of Philosophy

dissertationRecent advancements in mobile devices - such as Global Positioning System (GPS), cellular phones, car navigation system, and radio-frequency identification (RFID) - have greatly influenced the nature and volume of data about individual-based movement in space and time. Due to the prevalence of mobile devices, vast amounts of mobile objects data are being produced and stored in databases, overwhelming the capacity of traditional spatial analytical methods. There is a growing need for discovering unexpected patterns, trends, and relationships that are hidden in the massive mobile objects data. Geographic visualization (GVis) and knowledge discovery in databases (KDD) are two major research fields that are associated with knowledge discovery and construction. Their major research challenges are the integration of GVis and KDD, enhancing the ability to handle large volume mobile objects data, and high interactivity between the computer and users of GVis and KDD tools. This dissertation proposes a visualization toolkit to enable highly interactive visual data exploration for mobile objects datasets. Vector algebraic representation and online analytical processing (OLAP) are utilized for managing and querying the mobile object data to accomplish high interactivity of the visualization tool. In addition, reconstructing trajectories at user-defined levels of temporal granularity with time aggregation methods allows exploration of the individual objects at different levels of movement generality. At a given level of generality, individual paths can be combined into synthetic summary paths based on three similarity measures, namely, locational similarity, directional similarity, and geometric similarity functions. A visualization toolkit based on the space-time cube concept exploits these functionalities to create a user-interactive environment for exploring mobile objects data. Furthermore, the characteristics of visualized trajectories are exported to be utilized for data mining, which leads to the integration of GVis and KDD. Case studies using three movement datasets (personal travel data survey in Lexington, Kentucky, wild chicken movement data in Thailand, and self-tracking data in Utah) demonstrate the potential of the system to extract meaningful patterns from the otherwise difficult to comprehend collections of space-time trajectories

Modelling of interactions between rail service and travel demand: a passenger-oriented analysis

The proposed research is situated in the field of design, management and optimisation in railway network operations. Rail transport has in its favour several specific features which make it a key factor in public transport management, above all in high-density contexts. Indeed, such a system is environmentally friendly (reduced pollutant emissions), high-performing (high travel speeds and low values of headways), competitive (low unitary costs per seat-km or carried passenger-km) and presents a high degree of adaptability to intermodality. However, it manifests high vulnerability in the case of breakdowns. This occurs because a faulty convoy cannot be easily overtaken and, sometimes, cannot be easily removed from the line, especially in the case of isolated systems (i.e. systems which are not integrated into an effective network) or when a breakdown occurs on open tracks. Thus, re-establishing ordinary operational conditions may require excessive amounts of time and, as a consequence, an inevitable increase in inconvenience (user generalised cost) for passengers, who might decide to abandon the system or, if already on board, to exclude the railway system from their choice set for the future. It follows that developing appropriate techniques and decision support tools for optimising rail system management, both in ordinary and disruption conditions, would consent a clear influence of the modal split in favour of public transport and, therefore, encourage an important reduction in the externalities caused by the use of private transport, such as air and noise pollution, traffic congestion and accidents, bringing clear benefits to the quality of life for both transport users and non-users (i.e. individuals who are not system users). Managing to model such a complex context, based on numerous interactions among the various components (i.e. infrastructure, signalling system, rolling stock and timetables) is no mean feat. Moreover, in many cases, a fundamental element, which is the inclusion of the modelling of travel demand features in the simulation of railway operations, is neglected. Railway transport, just as any other transport system, is not finalised to itself, but its task is to move people or goods around, and, therefore, a realistic and accurate cost-benefit analysis cannot ignore involved flows features. In particular, considering travel demand into the analysis framework presents a two-sided effect. Primarily, it leads to introduce elements such as convoy capacity constraints and the assessment of dwell times as flow-dependent factors which make the simulation as close as possible to the reality. Specifically, the former allows to take into account the eventuality that not all passengers can board the first arriving train, but only a part of them, due to overcrowded conditions, with a consequent increase in waiting times. Due consideration of this factor is fundamental because, if it were to be repeated, it would make a further contribution to passengers’ discontent. While, as regards the estimate of dwell times on the basis of flows, it becomes fundamental in the planning phase. In fact, estimating dwell times as fixed values, ideally equal for all runs and all stations, can induce differences between actual and planned operations, with a subsequent deterioration in system performance. Thus, neglecting these aspects, above all in crowded contexts, would render the simulation distorted, both in terms of costs and benefits. The second aspect, on the other hand, concerns the correct assessment of effects of the strategies put in place, both in planning phases (strategic decisions such as the realisation of a new infrastructure, the improvement of the current signalling system or the purchasing of new rolling stock) and in operational phases (operational decisions such as the definition of intervention strategies for addressing disruption conditions). In fact, in the management of failures, to date, there are operational procedures which are based on hypothetical times for re-establishing ordinary conditions, estimated by the train driver or by the staff of the operation centre, who, generally, tend to minimise the impact exclusively from the company’s point of view (minimisation of operational costs), rather than from the standpoint of passengers. Additionally, in the definition of intervention strategies, passenger flow and its variation in time (different temporal intervals) and space (different points in the railway network) are rarely considered. It appears obvious, therefore, how the proposed re-examination of the dispatching and rescheduling tasks in a passenger-orientated perspective, should be accompanied by the development of estimation and forecasting techniques for travel demand, aimed at correctly taking into account the peculiarities of the railway system; as well as by the generation of ad-hoc tools designed to simulate the behaviour of passengers in the various phases of the trip (turnstile access, transfer from the turnstiles to the platform, waiting on platform, boarding and alighting process, etc.). The latest workstream in this present study concerns the analysis of the energy problems associated to rail transport. This is closely linked to what has so far been described. Indeed, in order to implement proper energy saving policies, it is, above all, necessary to obtain a reliable estimate of the involved operational times (recovery times, inversion times, buffer times, etc.). Moreover, as the adoption of eco-driving strategies generates an increase in passenger travel times, with everything that this involves, it is important to investigate the trade-off between energy efficiency and increase in user generalised costs. Within this framework, the present study aims at providing a DSS (Decision Support System) for all phases of planning and management of rail transport systems, from that of timetabling to dispatching and rescheduling, also considering space-time travel demand variability as well as the definition of suitable energy-saving policies, by adopting a passenger-orientated perspective

Investigating individual preferences for new mobility services: the case of “mobility as a service” products

In just a few years, the Mobility as a Service (MaaS) concept has gone from an idea discussed by very few, to being a prominent topic in any transportation related debate. However, within this time, there have only been few rigorous studies that explore the various aspects of MaaS. This thesis aims to contribute to existing knowledge by providing empirical evidence on individual preferences for MaaS plans and their components. In doing so, first desk-research is conducted to summarise existing MaaS schemes and outline the MaaS ecosystem. Next, MaaS surveys that are able to capture individual preferences for MaaS products are designed and specific challenges in the design process identified. The MaaS surveys, including MaaS plan stated preference experiments, are applied in two case study areas of London and Greater Manchester. Using the novel data collected, individual preferences for MaaS plans are examined using two distinct studies: (1) a mixed methods research conducted in London, which expands the survey by adding a qualitative (in-depth interview) element to examine user preferences for MaaS plans and the ways individuals choose between them; and (2) a latent class choice model based on data collected from Manchester to examine whether there is heterogeneity in preferences. Finally, implications for industry and policy stakeholders are discussed as well as interventions that can best support the widespread adoption of MaaS. The results of this thesis show there is interest in the concept of MaaS among potential users as many see value in a single app that integrates different transport modes into a single service. In general, individuals are hesitant in purchasing pre-payed MaaS plans and would be more comfortable with a pay-as-you-go product option. While many people are reluctant towards MaaS plans, the results indicate that heterogeneity exists in preferences towards them and there are different user groups based on socio-demographic characteristics and current mobility habits. Smaller, less expensive plans including modes such as public transport and bike sharing can be used to target students or middle-income people with have high overall mode usage. Larger, more expensive plans that include modes such as taxi and car sharing in addition to public transport, will be attritive to individuals who are likely younger, male, well-educated, have higher income and already use many transport modes. Older population groups, individuals with low income and those that do not use any transport modes or are uni-modal are least likely to adopt MaaS plans. The thesis also provides insights into individuals’ preferences towards transport modes within MaaS plans. The analysis showed that respondents classify modes within MaaS plans into three categories: ‘essential’ modes that are pivotal to the individual and which they most likely already frequently use; ‘considered’ modes are those that they would be willing to include but may not yet use; and ‘excluded’ modes are those that they definitely do not want in their plans and would eliminate any plan that included these. Public transport consistently proved to be an essential mode, while taxi, car sharing and bike sharing could be ‘essential’, ‘considered’ or ‘excluded’ depending on the characteristics of the individual. The main contributions of this thesis are the novel data collected in two case study cities about individuals’ preferences for MaaS plans and the findings gained through the analysis providing insights into possible target audiences and product designs for MaaS plans

BILEVEL LINEAR PROGRAMMING MODELS AND ALGORITHMS FOR FREIGHT TRANSPORTATION

2000/2001Ogni sistema di trasporto delle merci si presenta generalmente molto articolato e complesso: in particolare l'esistenza di numerosi soggetti che, a diverso livello e con diversi obiettivi, sono tenuti ad operare decisioni rappresenta un elemento che influisce in maniera spesso importante sull'assetto del sistema stesso. Il lavoro prende in esame un sistema di trasporto merci con due attori, denominati P e Q, che attraverso le rispettive decisioni determinano l'assetto dei flussi sulla rete. Il soggetto P, in particolare, è incaricato di soddisfare una data domanda di trasporto (ad esempio espressa mediante una matrice 0/D data) e può decidere come ripartire i flussi su una rete multi modale della quale percepisce i tratti fondamentali. Al momento della sua decisione, P conosce il costo generalizzato degli archi della rete e cerca di minimizzare il costo totale del trasporto. Inoltre il giocatore P deve rispettare le decisioni del giocatore Q. Il giocatore Q, che controlla una porzione della rete che connette le origini alle destinazioni di P, invece conosce il profitto unitario che deriva dal transito veicolare sui suoi archi e cerca di massimizzare il proprio profitto complessivo. Nel far questo può modificare la capacità degli archi della sua sotto rete, ma anch'egli deve comunque soddisfare la condizione di bilanciamento ai nodi e deve rispettare le decisioni di P. Quale primo elemento di originalità del presente lavoro può essere considerato il tentativo di condensare in un unico approccio alcuni elementi presenti singolarmente in filoni diversi. Infatti, tra i modelli della letteratura che intendono rappresentare esplicitamente le dinamiche decisionali interattoriali si ricordano i modelli multiattoriali sequenziali, i giochi su rete e la programmazione lineare bilivello i quali formano il quadro di riferimento in cui la presente lavoro si inserisce. Il quadro attoriale appena delineato offre l'opportunità di affrontare una serie di problemi diversi, nel campo dell'affidabilità della rete, a seconda dell'ordine con il quale i due giocatori decidono. Infatti il caso in cui la decisione di P preceda quella di Q può essere significativo, per P, al fine di valutare la peggiore situazione che potrebbe presentarsi per effetto di Q una volta stabilito l'assetto dei flussi sulla propria rete. È questo un tipico esempio della cosiddetta "worst case analysis. Viceversa, se gioca prima Q, P riesce a determinare il migliore assetto dei propri flussi nel rispetto di vincoli imposti da Q su una parte della rete interposta tra la sua origine e la destinazione. Si pensi ad esempio alla problematica dell'attraversamento di Paesi, quali Austria e Svizzera, che impongono severe limitazioni per i veicoli pesanti. Il problema descritto viene formulato come un gioco su rete nel quale i due giocatori, P e Q, non cooperano tra loro. Si ottiene così una formulazione di programmazione lineare bilivello (BLP) dove il giocatore che gioca per primo è il leader, mentre l'altro assume il ruolo di follower. Ricordando che i problemi BLP sono NPhard, è stato sviluppato ed implementato un algoritmo euristico di ricerca della soluzione ottima. Sfruttando però l'osservazione che, nel particolare caso in questione, la soluzione ottima del problema BLP è anche un punto di equilibrio di Nash, l'algoritmo restringe la sua ricerca nell'insieme dei punti di equilibrio di Nash. Da un punto di equilibrio di Nash si passa ad un altro corrispondente ad una soluzione "migliore per il leader fino a quando l'algoritmo non si ferma. Purtroppo però non si è sempre in grado di determinare un ottimo globale, ma solamente un ottimo locale individuando così, nel caso sia P a giocare per primo, un limite superiore alla soluzione ottima. Lo studio di tale modello è stato motivato dalla volontà di rappresentare, con riferimento al sistema del trasporto merci su gomma tra la Thrchia e l'Europa Occidentale, la situazione che si è venuta a creare nella regione dei Balcani a causa dei recenti eventi bellici. Tra le due regioni, annualmente, si registra un traffico dell'ordine delle centinaia di migliaia di veicoli commerciali. Per ragioni di semplicità, si è fatto riferimento alla sola componente verso l'Europa, fermo restando che la direzione opposta potrebbe essere analizzata in maniera del tutto analoga. Nell'esempio affrontato, la domanda di trasporto delle merci, che viene misurata in numero di veicoli all'anno, e che si sposta con origini diverse nel Sud-Est asiatico e destinazioni pure diverse nell'Europa Occidentale, è stata concentrata in due sole polarità (1 origine e l destinazione). Nel sistema appena descritto l'Associazione Industriali della nazione di origine (UND) svolge il ruolo di decisore centrale ed è stata assimilata al giocatore P di cui sopra. In breve, nota la domanda da trasportare, l'UND decide la distribuzione delle merci tra vari percorsi sulla rete che collega l'origine (Turchia) alla destinazione (Europa occidentale). Conosce pure il costo generalizzato degli archi di tale rete e opera le proprie decisioni con l'obiettivo di rendere minimo il costo del trasporto. L'evento bellico ha causato, come riflesso su detto sistema, una decisa modifica alla capacità degli archi di una porzione della rete stradale iniziale, che garantiva la connessione tra origine e destinazione. Alcuni archi sono stati eliminati (la rispettiva capacità posta pari a zero), altri hanno subito una netta riduzione della capacità, o un significativo aumento del costo generalizzato. La guerra quindi ha assunto un comportamento analogo a quello del giocatore Q. In questo caso però, non ha significato parlare di un'utilità che la guerra cerca di massimizzare secondo quanto esposto in precedenza, a meno che non si proceda ad assimilare l'utilità del giocatore Q con i costi di P: se Q gioca per massimizzare la propria utilità e quest'ultima corrisponde ai costi di P, automaticamente Q gioca per massimizzare i costi di P e il modello acquista proprio il significato di una analisi del caso peggiore per P. La rete considerata è stata semplificata in accordo con il livello di dettaglio delle informazioni di cui dispone P ed è formata da 99 nodi e 181 archi, di cui solamente 100 sotto il controllo di P. Gli altri 81 archi, concentrati nella regione dei Balcani, sono sotto il controllo di Q e costituiscono una sottorete connessa, che disconnette l'origine dalla destinazione. La capacità degli archi è stata determinata in accordo con il numero dei permessi di transito annui che ogni Stato concede ai veicoli turchi. Tale numero viene annualmente definito, mediante contrattazione tra le parti, in accordi bilaterali. In questa fase non si è tenuto conto delle differenti tipologie di permessi. In accordo con alcune necessarie ipotesi semplificative, la rete stessa è aciclica. I valori del costo per veicolo percepito da parte di P per transitare sugli archi della sottorete propria od altrui rispettivamente, sono stati determinati come funzione del costo monetario, della lunghezza fisica dell'arco e del tempo di percorrenza, tenendo in considerazione le varie voci che concorrono alla formazione del costo unitario (per veicolo-chilometro) di produzione di un servizio di trasporto sull'arco preso in esame. Per quanto riguarda i termini che compaiono nella funzione obiettivo di Q, si suppone che la guerra non tragga beneficio alcuno dal transito dei flussi veicolari sulla rete di P, mentre il profitto di Q è stato posto pari al costo sostenuto da P cambiato di segno come descritto in precedenza. Ai fini di valutare le prestazioni dell'algoritmo, il medesimo problema, viste le sue contenute dimensioni, è stato risolto anche con un algoritmo esatto, cioè in grado di determinare l'ottimo globale. Il risultato dell'algoritmo proposto si discosta di solo lo 0,3% dal risultato ottenuto con una procedura di branch and bound. L'esempio applicativo ha consentito di comprendere le potenzialità dell'approccio proposto e nell'ottica di un suo utilizzo concreto ha fornito delle utili indicazioni su possibili sviluppi da intraprendere legati sia all'algoritmo, sia al modello sia al caso di studio. In conclusione, il lavoro presenta un modello per la definizione dell'assetto del sistema di trasporto delle merci, con la trattazione esplicita delle dinamiche decisionali interattoriali. In particolare si prendono in considerazione due soggetti, che operano scelte in sequenza gerarchica, uno dei quali agisce per minimizzare i costi totali del trasporto e l'altro cerca invece di massimizzare il proprio profitto che dipende dal volume di traffico lungo gli archi sotto il suo controllo. Si propone una formulazione di programmazione lineare bilivello, per risolvere un gioco infinito statico non cooperativo con insiemi di vincoli accoppiati. Sono descritte le condizioni di esistenza e alcune proprietà dei punti di equilibrio di N ash, dalle quali discende un algoritmo di ricerca di un ottimo locale. Viene infine discussa un'applicazione del modello al caso del trasporto merci dalla Turchia all'Europa. Alcuni futuri sviluppi sono possibili. Essi portano alla progressiva eliminazione delle assunzioni semplificative che sono state adottate allo stato attuale nella formulazione del modello. In particolare si tratta della configurazione della rete, della struttura e delle proprietà dell'algoritmo (oggi trova solamente un ottimo locale). Inoltre si intende procedere con il perfezionamento del caso di studio.Freight transportation is generally a very complex domain where several players, each with its own set of objectives, act and operate at various decisional levels. There are different players in the field. The shippers who decide how much of each commodity to move from every origin to every destination and the means by which the goods will be moved. The carriers who respond to this transportation demands and route freight over the actual transportation network under their contro!. Finally, the government defined as the set of international, national and local authorities involved in any way with freight transportation via regulation and the provision of transportation infrastructure. In this work, we consider the case where only one shipper determines the demand for transportation over a network. However, he cannot decide fiow levels on arcs in a fully independent way due to the presence of a second agent controlling some links of the network and optimizing her own objective function. This situation is modelled as a game between two players P and Q acting o n the same network G. Player P fixes the fiows o n the arcs of G in such a way t ha t their divergence at some given nodes (sources and sinks) is equal to prescribed values. Such divergences may represent demand and availability levels for some commodity. On the other hand, player Q decides the values of the maximum capacities of some arcs of the network. Both players are interested in the fact that the connectivity between the sources and the sinks in the network is respected, i.e., they both want that the goods can reach their destination. However, they have different objectives. Player P aims at minimizing the transportation costs, whereas player Q aims at maximizing her profit (or, in generai, her utility) that is proportional to the fiow passing through the arcs under her control. Note that, in generai, the profit of player Q is not assumed to be equal to the cost of player P for the same are. Such game between players P and Q is modelled as a minimum cost flow problem for player P, where the are costs are given and the player Q decides the are capacities. The modelling of the games under investigation are mainly based upon three different research lines. First, the players understand the freight transportation system as a system where the actors involved do not act simultaneously and they explicitly take into account the sequential nature of the interactions among them. Second, they play a (hierarchical) game over a flow network which causes severe limitations and constraints to their action sets. Finally, the games exhibit linear characteristics and can be solved using bilevel linear programming. All these issues have already been discussed in the scientific literature, even though in different separate contexts. The merging of three mentioned approaches in only one single framework is a major contribution of our modelling perspective. Furthermore, bilevel programming is rich of theoretical results and numerica! algorithms, but is scare in actual applications. From this point of view, the present work might be considered as an interesting addition to the field. Bilevel noncooperative games in which one player ( called the leader) declares his strategy first an d enforces i t o n the other players ( called the followers) w ho react (rationally) to the leader's decision are referred to as Stackelberg games. Since the payoff functions and all the constraints in our Stackelberg games may be expressed in a linear form, these games will be formalized as bilevellinear programming problems (BLPPs). In generai, bilevel programming problems are difficult to sol ve because of their inherent non-convexity and non-differentiability. To face their NP-hard nature, we identify some properties of the game solutions which allow us to define a heuristic algorithm restricting its (local) search on the set of the Nash equilibrium points. The optimal solution of any BLPP lies on a vertex of the leader's inducible region. Relying on this result, we develop an algorithm which allows to move from a starting point of the shipper's inducible region to another point in the shipper's inducible region always providing a better solution for him. When no further better points may be attained, the algorithm stops. Unfortunately, only a local optimum is identified. The rationale behind the algorithm stems from the consideration that the optimal solution for our BLPP is also a Nash equilibrium point. In particular, the algorithm moves from a Nash equilibrium point to another better Nash equilibrium point of the BLPP under study. This framework may describe, as an example, the situation where restrictions are imposed by some alpine country on the number of trucks allowed to cross it by road each year. A different context involving the presence of a second agent o n the shipper's network occurred when the International Transporters' Association (UND) of Turkey had to face when the war in the Balkans started. This situation motivates our investigation on hierarchical noncooperative network games. The road freight traffi.c from Turkey to Centrai and Western Europe and viceversa suffered major disruptions because of the war in Balkans during the nineties. UND is the shipper controlling the quasi-totality of this traffi.c thus assuming the role of player P. H e had to cope with an "adverse entity" able to modify the available capacity on some specific links his vehicles had to pass through. The region involved in the confiict may be represented as a connected subnetwork disconnecting the origin and the destinations of the road transportation network since alternative road routes are not easily affordable. Other possibilities, like the seaborne links now operating, did not exist at that time. Hence the whole freight traffi.c was performed using a single mode of transport. The models developed in this work allow the shipper to perform a worst-case analysis at the strategie level for this situation assuming that player Q wishes to maximize the costs he has to afford when going through the region under her control. In fact, it is meaningless to talk about the utility or the profit the war may seek t o maximize. However, i t becomes a sensible modelling when the utility of player Q is strictly related to the costs afforded by player P on this portion of the network. lf player Q is maximizing her utility which corresponds to player P's costs, automatically she plays to maximize player P's costs. Hence the model represents a worst-case analysis for player P. A simple graph composed of 99 nodes and 181 arcs is presented. Player P controls a sub network composed of 100 arcs. The others 81 links representing the connections within the Balkans and Eastern Europe form a connected sub network. Only the main road links ha ve been considered ( motorways or highways). The capacities are calculated taking into account the total number of transit permits available for each country. This figure is annually fixed in bilatera! Joint Committee Meetings. Player P's costs are the average generalized costs derived as a function of lengths and transfer times in the physicallinks. Player Q does not have profits or losses for the fiows passing through the P zone and it is also assumed that the profits she earns for each unit of fiow going through the arcs under her control are equal to the costs afforded by the shipper when traversing these arcs. All the relevant data required to calculate these figures are collected in the UND Annual Sector Report 1997-98 (1999). The heuristic algorithm has been tested on this network and its results have been compared with the outcome obtained by using an exact enumeration procedure. Since it turns out that the percentage error of the heuristic algorithm is equal to 0,3%, we may claim that its performances are certainly highly satisfactory, at least in this specific example. Different extensions of the models and the algorithm developed may be easily envisaged both from the theoretical and the application side. These advances would provide either faster local or global search algorithms either more complete models representing in deeper detail the actual system and the interactions among the actors involved. Hence a decision support system for the shipper's decision making process at the strategie level can be built and effectively used by freight transportation practitioners.XIII Ciclo1969Versione digitalizzata della tesi di dottorato cartacea