Network topological effects on the macroscopic Bureau of Public Roads function

Cost flow functions are a central class of models in the transport field because they are an essential ingredient of static user equilibrium traffic assignment and transport policy and planning analysis. Macroscopic cost flow (MCF) functions, which model travel cost at different levels of network use, have gained much attention in recent decades due to their potential applications in area-wide traffic management and control, and initial land-use planning. They are the collective outcomes of the responses of road users to the existing transportation network and the interactions between road users at different levels of traffic demand. Network topological effects have long been anticipated to be the primary factors governing the shape and performance of a network. However, few studies have investigated network topology. This paper aims to unveil the direct link between network topological metrics and the parameters of a specific MCF, in the form of macroscopic Bureau of Public Roads (MBPR) function, with the support of real-world data. Seventy-one 1 km × 1 km urban built-up regions were sampled in Hong Kong. The MBPR functions of the selected regions were calibrated using taxi global positioning system data. Intensive investigations revealed that the average number of junctions per unit distance and the road density were topological features correlating with the free-flow travel time and congestion sensitivity parameters of the MBPR function, respectively. A spatially variable MBPR function was established.postprin

Systematic bias in transport model calibration arising from the variability of linear data projection

In transportation and traffic planning studies, accurate traffic data are required for reliable model calibration to accurately predict transportation system performance and ensure better traffic planning. However, it is impractical to gather data from an entire population for such estimations because the widely used loop detectors and other more advanced wireless sensors may be limited by various factors. Thus, making data inferences based on smaller populations is generally inevitable. Linear data projection is a commonly and intuitively adopted method for inferring population traffic characteristics. It projects a sample of observable traffic quantities such as traffic count based on a set of scaling factors. However, scaling factors are subject to different types of variability such as spatial variability. Models calibrated based on linearly projected data that do not account for variability may introduce a systematic bias into their parameters. Such a bias is surprisingly often ignored. This paper reveals the existence of a systematic bias in model calibration caused by variability in the linear data projection. A generalized multivariate polynomial model is applied to examine the effect of this variability on model parameters. Adjustment factors are derived and methods are proposed for detecting and removing the embedded systematic bias. A simulation is used to demonstrate the effectiveness of the proposed method. To illustrate the applicability of the method, case studies are conducted using real-world global positioning system data obtained from taxis. These data calibrate the Macroscopic Bureau of Public Road function for six 1 × 1 km regions in Hong Kong.postprin

Analysis and design of a high-voltage-gain hybrid switched-capacitor buck converter

This paper presents an analysis on the effect of having different number of capacitors n in the first-stage switched-capacitor circuit of an improved hybrid switched-capacitor buck converter for high-voltage-gain conversion. Various aspects of the topology, operation, and efficiency are investigated. It is shown both analytically and experimentally that a higher n in the step-down capacitor stage does not necessarily lead to an overall improved power efficiency. A design and optimization method is thus proposed for the improved SC-buck converter. © 2012 IEEE.published_or_final_versio

A series of exponential step-down switched-capacitor converters and their applications in two-stage converters

There is a demand for low-power high-voltage-gain transformerless DC-DC converters. It is difficult to achieve this kind of conversion with good efficiency through a buck converter. The two-stage converter is proven to be an effective solution for such applications. In this paper, a series of exponential step-down switched-capacitor (ESC) converters that achieve the benefits of high-voltage-gain conversion, but comprise fewer switches than other switched-capacitor converter topologies, is proposed. The ESC converters are applicable as first-stage converters in the two-stage power conversion solution. Experimental results validating the idea are provided. © 2013 IEEE.published_or_final_versio

A cell-based logit-opportunity taxi customer-search model

This paper proposes a cell-based model to predict local customer-search movements of vacant taxi drivers, which incorporates the modeling principles of the logit-based search model and the intervening opportunity model. The local customer-search movements were extracted from the global positioning system data of 460 Hong Kong urban taxis and inputted into a cell-based taxi operating network to calibrate the model and validate the modeling concepts. The model results reveal that the taxi drivers’ local search decisions are significantly affected by the (cumulative) probability of successfully picking up a customer along the search route, and that the drivers do not search their customers under the random walk principle. The proposed model helps predict the effects of the implementation of the policies in adjusting the taxi fleet size and the changes in passenger demand on the customer-search distance and time of taxi drivers

Bi-level decisions of vacant taxi drivers traveling towards taxi stands in customer-search: Modeling methodology and policy implications

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Sequential Logit Approach to Modeling Customer-searching Decisions of Taxi Drivers

Fulltext link: http://easts.info/on-line/proceedings/vol9/PDF/P137.pdfThis paper develops an enhanced sequential logit model to depict the customer-search behavior of vacant-taxi drivers. This model considers that vacant-taxi drivers can change the choices they make on their way to a designated district. Trip data from the global positioning systems (GPSs) of 460 urban taxis were extracted to calibrate the model and verify the factors underlying the drivers’ search decisions. The findings reveal that the proposed sequential logit model is capable of predicting the search paths of vacant-taxi drivers. This model form is considered more informative for policymakers who aim to study search paths and the associated traffic congestion contributed by taxis in each district

Application of novel D²T control to single-switch two-output switching power converters

Author name used in this publication: Chi K. Tse2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Design of symmetrical Class E power amplifiers for very low harmonic-content applications

Author name used in this publication: Chi K. Tse2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Dynamic traffic assignment: model classifications and recent advances in travel choice principles

Dynamic Traffic Assignment (DTA) has been studied for more than four decades and numerous reviews of this research area have been conducted. This review focuses on the travel choice principle and the classification of DTA models, and is supplementary to the existing reviews. The implications of the travel choice principle for the existence and uniqueness of DTA solutions are discussed, and the interrelation between the travel choice principle and the traffic flow component is explained using the nonlinear complementarity problem, the variational inequality problem, the mathematical programming problem, and the fixed point problem formulations. This paper also points out that all of the reviewed travel choice principles are extended from those used in static traffic assignment. There are also many classifications of DTA models, in which each classification addresses one aspect of DTA modeling. Finally, some future research directions are identified.postprin