Dynamic OD estimation in congested networks: theoretical findings and implications in practice

in Transportmetrica (2013), 9(6), 494-513

In this study we analyse the impact of congestion in dynamic origin–destination (OD) estimation. This problem is typically expressed using a bi-level formulation. When solving this problem the ... [more ▼]

In this study we analyse the impact of congestion in dynamic origin–destination (OD) estimation. This problem is typically expressed using a bi-level formulation. When solving this problem the relationship between OD flows and link flows is linearised. In this article the effect of using two types of linear relationship on the estimation process is analysed. It is shown that one type of linearisation implicitly assumes separability of the link flows, which can lead to biased results when dealing with congested networks. Advantages and disadvantages of adopting non-separable relationships are discussed. Another important source of error attributable to congestion dynamics is the presence of local minima in the objective function. It is illustrated that these local minima are the result of an incorrect interpretation of the information from the detectors. The theoretical findings are cast into a new methodology, which is successfully tested in a proof of concept. [less ▲]

Dynamic Origin-Destination Matrix Estimation on Large-Scale Congested Networks Using A Hierarchical Decomposition Scheme

in Journal of Intelligent Transportation Systems (2014), 18(1), 51-66

Despite the ever increasing computing power, dynamic Origin-Destination (OD) estimation in congested networks remains troublesome. In previous research, we have shown that an unbiased estimation requires ... [more ▼]

Despite the ever increasing computing power, dynamic Origin-Destination (OD) estimation in congested networks remains troublesome. In previous research, we have shown that an unbiased estimation requires the calculation of the sensitivity of the link flows to all Origin Destination flows, in order to incorporate the effects of congestion spillback. This is however computationally infeasible for large-scale networks. To overcome this issue, we propose a hierarchical approach for off-line application that decomposes the dynamic OD estimation procedure in space. The main idea is to perform a more accurate dynamic OD estimation only on subareas where there is congestion spillback. The output of this estimation is then used as input for the OD estimation on the whole network. This hierarchical approach solves many practical and theoretical limitations of traditional OD estimation methods. The main advantage is that different OD estimation method can be used for different parts of the network as necessary. This allows applying more advanced and accurate, but more time consuming methods only where necessary. The hierarchical approach is tested on a study network and on a real network. In both cases the proposed methodology performs better than traditional OD estimation approaches, indicating its merit. [less ▲]

Dynamic Pricing in the Presence of Myopic and Strategic Consumers: Theory and Experiment

in Production and Operations Management (2017), 26(1), 116--133

Dynamic Pricing Strategies in the Carsharing Business, Profit Maximization and Equity Considerations

Doctoral thesis (2021)

In the last two decades the development of mobile technology and the ease of access to an internet connection helped the consolidation of the sharing economy paradigm. This new way of purchasing goods and ... [more ▼]

In the last two decades the development of mobile technology and the ease of access to an internet connection helped the consolidation of the sharing economy paradigm. This new way of purchasing goods and services differs from old traditional business models since it enables a shared use of resources in order to save money and generate profit. As an important player in the sharing economy, sharing mobility continues, nowadays, to shape urban mobility with the introduction of different modes of shared transport such as carsharing, bike sharing, ride sourcing, and other collective mobility services. Different stakeholders participate in the creation and exploitation of these new mobility services: governmental agencies, customers, and private companies. Each of them has a specific purpose that can affect and stir the benefit of sharing platforms. Focusing on the carsharing service, on the business side and on the user side, profit and customer satisfaction are usually the main goals even if, at times, both difficult to pursue together. Competition on today's landscape leaves little room for both established and less established businesses. Opportunities to increase corporate profit become scarcer and more refined systems to better manage carsharing operations are needed to guarantee commercial viability. Evaluating business models for carsharing is no trivial task. Several methods are used for assessing the quality of changes in some operations or to evaluate possible approaches. Combinatorial and stochastic optimization are used to answer decision-making problems in the case of deterministic or uncertain problems. The shortcoming of these approaches is that they are limited at solving problems related to fleet management or service planning as it is more difficult to have an overview in which multiple properties (e.g., demography, territorial distribution, specificity of the fleet, ...) of both supply and demand are considered. This happens because car sharing is a highly complex service that has many interdependent factors. Given this complexity, a more favorable approach to estimate the demand for the service - together with all its peculiarities - and to help operators in the decision-making process, is the simulation one. This criterion allows the interaction of multiple factors which, through functional relationships between the decision-making parameters of the supplier, can introduce indicators to evaluate the quality of the solutions that cannot be easily derived analytically. This dissertation focuses on a simulation-based approach that aims to create a decision support system for carsharing business. This decision support system aims to use demographic and land use data as input, once the provider's needs are known, and to return solutions regarding the optimization of the carsharing service. The development of this thesis is conceived from the point of view of the service provider, even if considerations regarding the equity of the various strategies proposed therein for the service customers constitute an integral and fundamental part of the construction of this system of support for decisions. In this manuscript, we discuss the introduction of different dynamic pricing strategies that aim to increase the profit of the carsharing service, along with other indicators such as the number of bookings and utilization time of vehicles. By developing different price models, the introduction of dynamic prices based on the quantity of vehicles present in the station at the time of booking is evaluated and the output of the implementation of a dynamic price based on the time of the day is examined. In the first part of this thesis, we discuss how it is possible to evaluate the quality of a carsharing service from the point of view of its members, focusing on how different strategies generate or can reduce inequalities due to different wages or purchasing powers. Furthermore, using data collected by a car-sharing company operating in Germany and the United Kingdom, Oply, we implement these same strategies in a scenario calibrated with real data. Finally, we propose a methodology for calibrating carsharing scenarios in an agent-based environment.Moreover, we use these scenarios to demonstrate how it is possible, once there is complete knowledge of the demand and the status of the offer, to attribute a certain price to a single booking that maximizes the profit of the service. The overall results show that the introduction of dynamic pricing strategies does not always benefit all segments of the population and that the goals of a carsharing company are not always compatible with those of its members. Furthermore, they show how it is possible to increase the profit of a carsharing company accordingly to its position on the market, whether it has a total knowledge of the territory or not, whether it is an established company or not yet fully established. As we will also see in the final chapter of this thesis, the product of this work does not consist only in a practical contribution aimed mostly at carsharing companies, but also in a scientific counterpart that outlines new research directions. [less ▲]

Dynamic problem solving competency: More than intelligence?

Scientific Conference (2011, July 05)

Dynamic problem solving. Multiple-item testing based on minimal complex systems.

in Leutner, Detlev; Fleischer, Jens; Grünkorn, Jiliane (Eds.) et al Competence assessment in education : Research, models, and instruments. (2017)

Dynamic Problem Solving: A new measurement perspective

in Applied Psychological Measurement (2012), 36

This article addresses two unsolved measurement issues in dynamic problem solving (DPS) research: (a) unsystematic construction of DPS tests making a comparison of results obtained in different studies ... [more ▼]

This article addresses two unsolved measurement issues in dynamic problem solving (DPS) research: (a) unsystematic construction of DPS tests making a comparison of results obtained in different studies difficult and (b) use of time-intensive single tasks leading to severe reliability problems. To solve these issues, the MicroDYN approach is presented, which combines (a) the formal framework of linear structural equation models as a systematic way to construct tasks with (b) multiple and independent tasks to increase reliability. Results indicated that the assumed measurement model that comprised three dimensions, information retrieval, model building, and forecasting, fitted the data well (n = 114 students) and could be replicated in another sample (n = 140), showing excellent reliability estimates for all dimensions. Predictive validity of school grades was excellent for model building but nonexistent for the other two MicroDYN dimensions and for an additional measure of DPS. Implications are discussed. [less ▲]

Dynamic problem solving: Just intelligence or something different?

Scientific Conference (2011, September)

Dynamic protonation equilibrium of solvated acetic acid

in Angewandte Chemie International Edition (2007), 46(16), 2939-2943

Dynamic regulation of microRNA expression following interferonγ- induced gene transcription

in RNA Biology (2012), 9(7), 987-989

MicroRNAs are major players in post-transcriptional gene regulation. Even small changes in miRNA levels may have profound consequences for the expression levels of target genes. Hence, miRNAs themselves ... [more ▼]

MicroRNAs are major players in post-transcriptional gene regulation. Even small changes in miRNA levels may have profound consequences for the expression levels of target genes. Hence, miRNAs themselves need to be tightly, albeit dynamically, regulated. Here, we investigated the dynamic behavior of miRNAs over a wide time range following stimulation of melanoma cells with interferonγ (IFNγ), which activates the transcription factor STAT1. By applying several bioinformatic and statistical software tools for visualization and identification of differentially expressed miRNAs derived from time-series microarray experiments, 8.9% of 1105 miRNAs appeared to be directly or indirectly regulated by STAT1. Focusing on distinct dynamic expression patterns, we found that the majority of robust miRNA expression changes occurred in the intermediate time range (24-48 h). Three miRNAs (miR-27a, miR-30a and miR-34a) had a delayed regulation occurring at 72 h while none showed significant expression changes at early time points between 30 min and 6 h. Expression patterns of individual miRNAs were altered gradually over time or abruptly increased or decreased between two time points. Furthermore, we observed coordinated dynamic transcription of most miRNA clusters while few were found to be regulated independently of their genetic cluster. Most interestingly, several "star" or passenger strand sequences were specifically regulated over time while their "guide" strands were not. © 2012 Landes Bioscience. [less ▲]