IMPROVING THE RELIABILITY OF A TWO-STEPS DYNAMIC DEMAND ESTIMATION APPROACH BY SEQUENTIALLY ADJUSTING GENERATIONS AND DISTRIBUTIONS

Poster (2015, January 16)

Systematic assessment of local & global signal control policies: A methodological perspective

in Proceedings of 2015 International Conference on Models and Technologies for Intelligent Transportation Systems, MT-ITS 2015 (2015)

Traffic control performance on networks depends on the flow response to the policy adopted, which in turn contributes to determine the optimal signal settings. This paper focuses on the relationship ... [more ▼]

Traffic control performance on networks depends on the flow response to the policy adopted, which in turn contributes to determine the optimal signal settings. This paper focuses on the relationship between local and network wide traffic control policies within the combined traffic control and assignment problem. Through a full exploration of the solution space, an in depth cross comparison is performed between the well-known local policies P0 and Equisaturation, versus the global policies Maximum Throughput and Minimum Delay, to verify how the two local policies approximate the optimal settings for signalized intersections. Realistic traffic dynamics, such as congestion, multiple controllers and spillback are considered, to empirically determine the conditions under which the local policies are able to approximate global performances. After presenting the different local and global control policies, experiments are performed on simple toy networks. The complexity of the underlying network and, therefore, of the problems' boundary conditions is then increased, allowing us to showcase how the different metrics perform in different situations. Finally, conclusions on the results are drawn. © 2015 BME. [less ▲]

Assessing partial observability in network sensor location problems

in Transportation Research. Part B : Methodological (2014), 70

The quality of information on a network is crucial for different transportation planning and management applications. Problems focusing on where to strategically extract this information can be broadly ... [more ▼]

The quality of information on a network is crucial for different transportation planning and management applications. Problems focusing on where to strategically extract this information can be broadly subdivided into observability problems, which rely on the topological properties of the network, and flow-estimation problems, where (prior) information on observed flows is needed to identify optimal sensor locations. This paper contributes mainly to the first category: more specifically, it presents a new methodology and an intuitive metric able to quantify the quality of a solution in case of partial observability, i.e. when not all flow variables are observed or can be uniquely determined from the observed flows. This methodology is based on existing approaches that can efficiently find solutions for full observability (i.e., the set of sensors needed to make the system fully determined), and exploits only the algebraic relations between link, route and origin-destination flow variables to quantify the information contained in any arbitrary subset of these variables. The new metric allows, through its adoption within simple search algorithms, to efficiently select sensor locations when the number of available sensors is limited by, for example, budget constraints and is less than the number needed to guarantee full observability. The chosen positions aim at selecting those locations that contain the largest information content on the whole network. This is an important contribution in this field, since even in small sized networks the solution for full observability requires an exceedingly large amount of sensors. The assessment of partial observability solutions, based on explicit route enumeration, allows one to categorize families of full observability solutions, and shows that these contain different information potential. This way, it is possible to rank solutions requiring a lower number of sensors while containing the same information content. We tested this new methodology both on toy networks, in order to analyse the properties of the metric and illustrate its logic, and to explain and test heuristic search algorithms for optimal sensor positioning on a real-sized network. Analysis of partial observability solutions shows that the basic search algorithms succeed in finding the links that contain the largest deal of information in a network. [less ▲]

A Joint Day-to-Day Mode and Within-Day Departure Time Choice Model for the Analysis of Dynamic Ridesharing

Scientific Conference (2014, June 19)

Sharing travels is an effective way to increase car occupancy rates and to reduce the total number of cars for the same distances travelled. A potentially attractive service based on the sharing concept ... [more ▼]

Sharing travels is an effective way to increase car occupancy rates and to reduce the total number of cars for the same distances travelled. A potentially attractive service based on the sharing concept is dynamic ridesharing (DRS), where a service provider matches up driver and passenger with similar itineraries and time schedules with an automated program. To analyse how modal shift from single passenger use of the car to high occupancy one can be realized and what are the demand management solutions that can effectively be recommended, we deal with a theoretically interesting basic model structure of a single-link case, in which we study the complex interaction of multiple factors involved in the dynamic ridesharing problem, and the joint sensitivity to the most relevant parameters involved in this behavioural process. The main contribution of this study is therefore a unified framework that is able to model the dynamics of the departure time, characterized as a within-day process, while keeping the mode choice as a day-to-day process, and characterizing explicitly the matching process of DRS. [less ▲]

A TWO-STEP APPROACH FOR THE CORRECTION OF THE SEED MATRIX IN THE DYNAMIC DEMAND ESTIMATION

in Transportation Research Record: Journal of the Transportation Research Board (2014), 2466

In this work deterministic and stochastic optimization methods are tested for solving the Dynamic Demand Estimation problem. All the adopted methods demonstrate the difficulty in reproducing the correct ... [more ▼]

In this work deterministic and stochastic optimization methods are tested for solving the Dynamic Demand Estimation problem. All the adopted methods demonstrate the difficulty in reproducing the correct traffic regime, especially if the seed matrix is not sufficiently close to the real one. Therefore, in this paper a new and intuitive procedure to specify an opportune starting seed matrix is proposed: it is a two-step procedure based on the concept of dividing the problem into small-size problems, focusing on specific OD pairs in different steps. Specifically, the first step focuses on the optimization of a subset of OD variables (the ones who generate the higher flows or the ones who generate the bottlenecks on the network). In the second step the optimization works on all the OD pairs, using as starting matrix the matrix derived from the first step. In this way is possible to use a more performance optimization method for every step, improving the performance of the method and the quality of the result with respect to the classical “one-step” approach. The procedure has been tested on the real network of Antwerp, Belgium, demonstrating its efficacy in combination with different optimization methods. [less ▲]

Models and Technologies for Intelligent Transportation Systems: new challenges and metaheuristic solutions for large-scale network applications

in Journal of Intelligent Transportation Systems (2014), 18(1), 1-4

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 ▲]

Evaluation of intervention strategies for a road link in the Netherlands

in Built Environment Project and Asset Management (2014), 4(2), 180-198

Purpose – The purpose of this paper is to investigate the use of the impact hierarchy and the optimization model to determine the optimal intervention strategy for a road link composed of multiple objects ... [more ▼]

Purpose – The purpose of this paper is to investigate the use of the impact hierarchy and the optimization model to determine the optimal intervention strategy for a road link composed of multiple objects. The paper focusses on the results of a case study of intervention project on A20 road link in Rotterdam, the Netherlands. Design/methodology/approach – The study was a case study research. It describes briefly the impact hierarchy and its link to the optimization model, and then focussed on analyzing the results obtained from running the model. In order to understand the influence of various factors affecting the results of optimization, sensitivity analysis was performed. Findings – The proposed hierarchy is suitable to be used to support the determination of optimal intervention strategies (OISs) for public road. From the case study, it was also realized that optimal intervention strategy can be changed due to not only intervention costs incurred by the owner, but also due to the setup of traffic configuration during the execution of interventions since the impacts incurred to users, directly affected public, and indirectly affected public are significantly different from one traffic configuration to the others. The optimal intervention strategy also depends greatly on the factors of deterioration during the operation of the infrastructure objects. Research limitations/implications – In the impact hierarchy, some impact factors are difficult to be quantified, e.g., the long-term economic impacts on the region where having intervention projects. The use of only exponential function for impacts could be oversimplified the actual behavior of the impacts. Other functional form should be investigated to be used within the framework of the optimization model. Practical implications – The proposed hierarchy and the optimization model could be used in practical situation for determination of OISs for multiple objects within a road link. Originality/value – This paper contributes to the body of knowledge of stakeholder analysis in the field of infrastructure asset management. It also gives a guideline and tool for infrastructure administrators to select the OISs for their infrastructure network. [less ▲]

Equilibrium and sensitivity analysis of dynamic ridesharing

Scientific Conference (2013)

Sharing travels is an effective way to increase car occupancy rates and to reduce the number of cars for the same distances traveled. This is a problem involving operations research (how to best match ... [more ▼]

Sharing travels is an effective way to increase car occupancy rates and to reduce the number of cars for the same distances traveled. This is a problem involving operations research (how to best match travels in time and space, what level of similarity for the routes,…) and behavior challenges (on which conditions users choose to share travels, which type of users is willing to share the travel, what is the accepted detour and rescheduling, …). This research aims at filling the gap in the latter aspect by proposing an equilibrium modeling approach for (dynamic) ridesharing. By using a Nested logit model, , greater insight into the impact of different policies, behavioral factors and matching criteria can be presented. We deal with a theoretically interesting basic model structure of a single-link case, in which we study the complex interaction of multiple factors, and the joint sensitivity to the most relevant parameters. This allows us to derive some basic recommendations from the equilibrium states reached. [less ▲]

A Null-Space metric for the analysis of partial network observability in sensor location problems

Scientific Conference (2013)