Dynamic origin–destination estimation in congested networks: theoretical findings and implications in practice

Abstract

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.

An enhanced SPSA algorithm for the calibration of Dynamic Traffic Assignment models

“…Furthermore, W-SPSA still suffers from some of the limitations associated with SPSA, such as the fact that it can still get trapped in local optima rather than finding the global optimum. The importance of a good initial solution in reducing the likelihood of getting stuck in a local optimum, especially in highly congested networks, has been pointed out by Frederix et al (2013). One way to overcome this limitation in practice is to re-initialize the algorithm with different initial solutions and observe whether the same solution is reached every time.…”

“…Finally, it would be interesting in terms of future research to consider and compare the relative merits and performance of the presented approach with other SPSA extensions and gradient approximation methods, which consider (implicitly) correlations, such as the work of Frederix et al (2013), Cipriani et al (2011), andCantelmo et al (2014).…”

The Influence of Assignment Criteria for the Solution of Dynamic Travel Demand Estimation

“…Generally Γ is reported in previous works of the authors as a Dynamic User Equilibrium (DUE) assignment; however similar approaches in literature adopt also Dynamic Network Loading (DNL) when there is no need for route choice (Frederix et al, 2013, Cantelmo et al, 2014 and non-equilibrium approaches.…”

W–SPSA in Practice: Approximation of Weight Matrices and Calibration of Traffic Simulation Models

“…Such knowledge is lost in applications of the original SPSA algorithm, when time-dependent, location-specific error terms are transformed into a single scalar. Besides SPSA extensions, other gradient approximation methods, which consider (implicitly) correlations, have also been proposed, such as the work of Frederix et al (2011Frederix et al ( , 2013.…”