Anthony Chen - Academia.edu (original) (raw)

Papers by Anthony Chen

ICCTP 2010, 2010

This paper proposes a new path finding model, called the α-reliable mean-excess model, to determi... more This paper proposes a new path finding model, called the α-reliable mean-excess model, to determine an optimal path with the minimum mean-excess travel time required to meet the user-specified reliability threshold α. The model explicitly considers both reliability and unreliability aspects of travel time variability in the travelers’ decision process. It provides a more accurate and complete picture in reflecting travelers’ risk preferences under an uncertain environment. The problem is formulated as a stochastic mixed-integer problem and solved by a double-relaxation scheme. Numerical results are presented to demonstrate the characteristics of the model as well as the solution algorithm.

Transportmetrica, 2010

Recently, a multi-objective model for locating the automatic vehicle identification (AVI) readers... more Recently, a multi-objective model for locating the automatic vehicle identification (AVI) readers in a transportation network was proposed by the authors along with its solution procedure. The model locates the AVI readers by simultaneously considering three objectives: the equipment and installation cost (e.g. number of AVI readers), the coverage of the AVI system (e.g. number of origin-destination (O-D) pairs), and the amount/quality of travel information obtained (e.g. number of AVI readings). However, only a single travel demand pattern for a certain time period, such as the evening peak hour, was considered in determining the AVI reader locations. Therefore, the recommended AVI system may not be able to guarantee the amount of travel information gathered during other time periods. This study extends our previously proposed model by developing three scenariobased models to accommodate different travel demand patterns observed during the whole day. A case study is provided to illustrate the applicability of the new models and the robustness of the AVI system designed by considering different travel demand patterns.

Transportation, 2012

Perceived mean-excess travel time is a new risk-averse route choice criterion recently proposed t... more Perceived mean-excess travel time is a new risk-averse route choice criterion recently proposed to simultaneously consider both stochastic perception error and travel time variability when making route choice decisions under uncertainty. The stochastic perception error is conditionally dependent on the actual travel time distribution, which is different from the deterministic perception error used in the traditional logit model. In this paper, we investigate the effects of stochastic perception error at three levels: (1) individual perceived travel time distribution and its connection to the classification by types of travelers and trip purposes, (2) route choice decisions (in terms of equilibrium flows and perceived mean-excess travel times), and (3) network performance measure (in terms of the total travel time distribution and its statistics). In all three levels, a curve fitting method is adopted to estimate the whole distribution of interest. Numerical examples are also provided to illustrate and visualize the above analyses. The graphical illustrations allow for intuitive interpretation of the effects of stochastic perception error at different levels. The analysis results could enhance the understanding of route choice behaviors under both (subjective) stochastic perception error and (objective) travel time uncertainty. Some suggestions are also provided for behavior data collection and behavioral modeling.

Transportation Research Record: Journal of the Transportation Research Board, 1999

Route planning and guidance (RPG) services are intended to provide benefits to their users, in th... more Route planning and guidance (RPG) services are intended to provide benefits to their users, in the form of either convenience or, more importantly, travel time savings. The reduction in system travel time, if achieved, is a “side effect.” How should the transportation management agency then respond to these services? Under what circumstances should the agency encourage or discourage their implementation? A model to answer these questions is developed. Two ingredients are important in the model discussed. First, the market penetration of RPG is modeled in an elastic manner. Analogous to a supply-demand equilibrium, market penetration is determined endogenously in an equilibrium between the benefits and cost of acquiring the services. It is argued that the cost of RPG services could be used as a way to alter the elastic market penetration, and hence modify and, it is hoped, lower the total system congestion. Thus, a bilevel program to capture the situation is formulated. The lower-lev...

Transportation Research Record: Journal of the Transportation Research Board, 2013

The transportation network design problem (NDP) is a high capital investment decision-making prob... more The transportation network design problem (NDP) is a high capital investment decision-making problem that inherently involves both subjective and objective uncertainties as well as multiple objectives. Goal programming is a practically useful approach with an explicit consideration of planners’ goal setting and priority structure among the multiple objectives. This paper describes the development of a hybrid goal programming (HGP) approach for modeling both subjective and objective uncertainties simultaneously in the NDP decision-making process. Planners’ subjective uncertainty regarding the linguistic setting of goals and priority structure is characterized as a set of fuzzy variables with nonlinear achievement and satisfaction functions, and the objective travel demand uncertainty is characterized as a set of random variables with predefined probability distributions. The HGP-NDP is formulated as a chance-constrained model in a bi-level programming framework and solved by a geneti...

Transportation Research Record: Journal of the Transportation Research Board, 2001

The Frank–Wolfe (FW) algorithm is the predominant algorithm used to solve traffic assignment prob... more The Frank–Wolfe (FW) algorithm is the predominant algorithm used to solve traffic assignment problems in transportation planning studies. Despite its slow convergence, it remains the most popular choice among practitioners and researchers. One reason for its popularity is that it requires very modest memory storage, which allows planners to solve networks of realistic sizes. Computer random-access memory storage has become extremely cheap, and it is possible to store more information in the FW algorithm to improve the speed of convergence. This information may be required anyway in certain applications, such as optimal routing in route guidance systems, analysis of environmental impact, nonadditive traffic equilibrium problems, and origin-destination matrix estimation. Different flow update strategies are used to examine how to effectively utilize the additional information to improve the performance of the FW algorithm. Implementation of three flow update strategies in the FW algor...

Transportation Research Record: Journal of the Transportation Research Board, 2002

The computational performance of five algorithms for the traffic assignment problem (TAP) is comp... more The computational performance of five algorithms for the traffic assignment problem (TAP) is compared with that of mid- to large-scale randomly generated grid networks. The applied procedures include the Frank-Wolfe, PARTAN, gradient projection, restricted simplicial decomposition, and disaggregate simplicial decomposition algorithms. A statistical analysis is performed to determine the relative importance of various properties (network size, congestion level, solution accuracy, zone-node ratio) of the traffic assignment problem for the five selected algorithms. Regression models, which measure central processing unit time and number of iterations consumed by each algorithm using various factors and their combinations, are derived to provide a quantitative evaluation. Ultimately, the findings of this research will be useful in guiding transportation professionals to choose suitable solution algorithms and to predict the resulting algorithm performance in TAPs.

Transportation Research Record: Journal of the Transportation Research Board, 2004

The problem of locating automatic vehicle identification (AVI) readers on a transportation networ... more The problem of locating automatic vehicle identification (AVI) readers on a transportation network is one worth considering. AVI readers are strategically located to catch a maximum number of trips and cover a maximum number of origin-destination (O-D) pairs using a minimum number of AVI readers. There are three possible objectives when deciding locations for AVI readers: (a) a minimum number of AVI readers, (b) maximum O-D coverage, and (c) a maximum number of trips (or AVI readings). To satisfy all three objectives as much as possible, the problem is formulated as a multiobjective integer-optimization problem. A distance-based genetic algorithm is applied to solve this multiobjective AVI reader-location problem by explicitly generating the nondominated solutions. Numerical results are presented to demonstrate the feasibility of the proposed multiobjective model. The procedure proposed holds great promise for the development of a well-configured AVI system that can achieve a balanc...

Transportation Research Record: Journal of the Transportation Research Board, 2010

Transportation agencies are increasingly interested in new strategies for integrated project deli... more Transportation agencies are increasingly interested in new strategies for integrated project delivery, such as design–build. When making a decision between a traditional design–bid–build delivery and an integrated project delivery such as design–build, the agency should consider potential cost savings, time savings, and quality improvements. To maximize the success of design–build projects, transportation agencies need to pay attention to several aspects of this system, including initial steps like contract procurement. Agencies should prepare for the procurement phase carefully on the basis of project size, complexity, timing, selection methods, and so on. This is especially important for design–build projects in which participating firms invest significant effort during the contract procurement phase while planning design and construction and assessing risks. To assist in improving the success of design–build projects, a study was conducted to analyze the relationship between dura...

Transportation Research Record: Journal of the Transportation Research Board, 2012

This paper develops path-based algorithms to solve the C-logit stochastic user equilibrium (SUE) ... more This paper develops path-based algorithms to solve the C-logit stochastic user equilibrium (SUE) problem on the basis of an adaptation of the gradient projection method. The algorithms' strategies for step size determination differ. Three strategies are investigated: (a) predetermined step size, (b) Armijo line search, and (c) self-adaptive line search. The algorithms are tested on the well-known Winnipeg (Manitoba, Canada) network. Two sets of experiments are conducted: (a) a computational comparison of different line search strategies and (b) the impact of different modeling specifications for route overlapping (a flow-independent or a flow-dependent commonality factor). The results indicate that the path-based algorithm with the self-adaptive step size strategy performs better than the other step size strategies. The paper shows that, depending on the model parameters, particularly the commonality factor parameter, the C-logit SUE flows may be quite different from the multino...

Transportation Research Part A: Policy and Practice, 2011

Flexibility of the transportation system is one of the important performance measures needed to d... more Flexibility of the transportation system is one of the important performance measures needed to deal with demand changes. In this paper, we provide a quantitative assessment of capacity flexibility for the passenger transportation network using bi-level network capacity models. Two approaches for assessing the value of capacity flexibility are proposed. One approach is based on the concept of reserve capacity, which reflects the flexibility with respect to changes in terms of demand volume only. The second approach allows for variations in the demand pattern in addition to changes in demand volume in order to more fully capture demand changes. Two models are developed in the second approach to consider two types of capacity flexibility. The total capacity flexibility allows all users to have both route choice and destination choice when estimating capacity flexibility. The limited capacity flexibility estimates how much more demand volume could be added to a fixed demand pattern by allowing the additional demand to deviate from the fixed demand pattern. Numerical examples are provided to demonstrate the different concepts of capacity flexibility for a passenger transportation system under demand changes.

Transportation Planning and Technology, 2013

Abstract Modeling the elasticity of travel demand in network equilibrium analysis has several imp... more Abstract Modeling the elasticity of travel demand in network equilibrium analysis has several important transportation applications. In this paper, we provide a mathematical programming formulation for the C-logit stochastic user equilibrium problem with elastic demand (CL-SUE-ED) in the route domain. The proposed model is capable of explicitly modeling the elasticity of travel demand and the effect of route overlapping on travel choice and route choice simultaneously. Some qualitative properties of the model, including the equivalency and uniqueness of the solution, are also rigorously proved. To solve the CL-SUE-ED model, a partial linearization method is developed to handle the elastic demand and route overlapping considerations. In addition, a self-regulated averaging stepsize scheme is adopted to smartly determine the stepsize while avoiding evaluating the complex objective function. Numerical examples are also provided to demonstrate the features of the proposed model and solution algorithm.

Transport Reviews, 2011

This paper aims to provide a state-of-the-art review of the transport network design problem (NDP... more This paper aims to provide a state-of-the-art review of the transport network design problem (NDP) under uncertainty and to present some new developments on a biobjective reliable network design problem (BORNDP) model that explicitly optimizes the capacity reliability and travel time reliability under demand uncertainty. Both are useful performance measures that can describe the supply-side reliability and demand side reliability of a road network. A simulation-based multi-objective genetic algorithm (SMOGA) solution procedure, which consists of a traffic assignment algorithm, a genetic algorithm, a Pareto filter, and a Monte-Carlo simulation, is developed to solve the proposed BORNDP model. A numerical example based on the capacity enhancement problem is presented to demonstrate the tradeoff between capacity reliability and travel time reliability in the NDP.

Journal of Transportation Engineering, 2012

AbstractThe goals of this paper are to (1) provide a review of the recently developed measures fo... more AbstractThe goals of this paper are to (1) provide a review of the recently developed measures for assessing the quality of origin-destination (O-D) trip tables estimated from traffic counts and (2) propose a new generalized demand scale (GDS) measure. This GDS quality measure generalizes the total demand scale (TDS) quality measure by allowing the assessment of the intrinsic underdeterminant problem of O-D estimation from traffic counts at various spatial levels. Numerical examples are provided to compare the proposed GDS measure with the TDS measure, the maximal possible relative error, and the expected relative error and to illustrate the features of the GDS measure.

Journal of Transportation Engineering, 2013

This study establishes a mathematical model that can represent the conflicting effects of two ped... more This study establishes a mathematical model that can represent the conflicting effects of two pedestrian streams with an oblique intersecting angle in a large crowd. In a previous study, a controlled experiment in which two streams of pedestrians were asked to walk in designated directions was used to model the bi-directional pedestrian stream of certain intersecting angles. In this study, we revisit that problem and apply the Bayesian inference approach to calibrate an improved model with the controlled experiment data. We also collected pedestrian movement data from a busy crosswalk using a video observation approach. The two sets of data are used separately to calibrate our proposed model. With the calibrated model, we study the relationship between speed, density, and flow in both the reference and conflicting streams, and predict how these factors affect the interactions of moving pedestrian streams. We find that the speed of one stream not only decreases with its total density, but it also decreases with the ratio of its flow in relation to the total flow, i.e., the speed of the pedestrians decreases if their stream changes from the major to the minor stream. We also observe that the maximum disruption induced by pedestrian flow from an intersecting angle occurs when the angle is near 135.

Journal of Transportation Engineering, 2005

Path flow estimator ͑PFE͒ is a one-stage network observer proposed in the transportation literatu... more Path flow estimator ͑PFE͒ is a one-stage network observer proposed in the transportation literature to estimate path flows and path travel times from traffic counts in a transportation network. The estimated path flows can further be aggregated to obtain the origin-destination ͑O-D͒ flows, which are usually required in many transportation applications. In this paper, we examine the capability of PFE in capturing the total demand of the study network as well as individual O-D demands. Numerical examples are provided to show the effects of the number and locations of traffic counts on the quality of O-D estimates. The results indicate that PFE has the potential to correctly estimate the total demand when proper observations, in terms of the number and their locations, are provided. In general, the spatial distribution of O-D demands is difficult to estimate even when traffic counts are available on all network links.

Journal of Construction Engineering and Management, 2014

ABSTRACT Most construction safety management processes rely on the hazard recognition capability ... more ABSTRACT Most construction safety management processes rely on the hazard recognition capability of workers. Hazards that remain unidentified can potentially result in catastrophic injuries and illnesses. As such, thorough hazard recognition is fundamentally essential to protect the health and well-being of the construction workforce. Despite its importance, recent research indicates that a large proportion of hazards remain unrecognized, exposing workers to unmitigated risks. Surprisingly, safety research has not adequately focused on developing specialized strategies to develop construction worker competency in hazard recognition. This paper reports a two-year research effort with the following objectives: (1) develop a high-fidelity augmented virtual environment [System for Augmented Virtuality Environment Safety (SAVES)] that helps develop workers&#39; hazard recognition skill through risk-free learning and immediate feedback; (2) embed cognitive retrieval mnemonics to improve long-term retention of cues for construction hazards; (3) evaluate the effectiveness of the strategy as an intervention on active construction crew by using the multiple baseline testing approach. The first two objectives were accomplished through a combined effort from a panel of 14 subject matter experts and five academic researchers. This was followed by field experiments to test the hypothesis that the experience with SAVES improves the proportion of hazards identified by participants during subsequent field operations. The findings revealed that crews, on average, were able to only identify 46% of hazards prior to the introduction of the intervention, but were able to recognize 77% of hazards in the postintervention phase. This study represents the first endeavor to measure the effectiveness of augmented virtuality and serious gaming in developing hazard signal detection skills in construction field settings. (C) 2014 American Society of Civil Engineers.

Journal of Chromatography A, 1996

Capillary isoelectric focusing (cIEF) and IEF of recombinant humanized monoclonal antibody HER2 (... more Capillary isoelectric focusing (cIEF) and IEF of recombinant humanized monoclonal antibody HER2 (rhuMAbHER2) show five charged isoforms with estimated pI values ranging from 8.6-9.1. The cIEF assay demonstrated good precision with relative standard deviations (R.S.D.) 0.7-3.7% and 0.4-4.2% for intra and interassay analysis, respectively. The method was linear for the area of the main peak over the concentration range 2-250 micrograms/ml with a Pearson correlation coefficient > 0.99. The limit of detection for the main peak was determined to be 2 ppm. With both sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) and SDS-polyacrylamide gel electrophoresis, the nonreduced rhuMAbHER2 migrated as a single major peak with minor peaks in the aggregate and clip regions. After reduction, the electropherogram and the slab gel showed the expected heavy chain and light chain fragments with minor peaks in the aggregate and clip regions. The SDS-CGE assay showed good precision with R.S.D. values of 0.1-7.8% and 0.1-8.1% for intra and interassay analysis, respectively. The Pearson correlation coefficient for the area of the main peak was > 0.99 demonstrating linearity for the concentration range 0.5-500 micrograms/ml. The limit of detection for intact rhuMAbHER2 was determined to be 0.5 ppm. The data presented demonstrates the feasibility of replacing the slab gel techniques with capillary electrophoresis in a quality control environment.

Journal of Advanced Transportation, 2012

Recent empirical studies have revealed that travel time variability plays an important role in tr... more Recent empirical studies have revealed that travel time variability plays an important role in travelers' route choice decisions. To simultaneously account for both reliability and unreliability aspects of travel time variability, the concept of mean-excess travel time (METT) was recently proposed as a new riskaverse route choice criterion. In this paper, we extend the mean-excess traffic equilibrium model to include heterogeneous risk-aversion attitudes and elastic demand. Specifically, this model explicitly considers (1) multiple user classes with different risk-aversions toward travel time variability when making route choice decisions under uncertainty and (2) the elasticity of travel demand as a function of METT when making travel choice decisions under uncertainty. This model is thus capable of modeling travelers' heterogeneous risk-averse behaviors with both travel choice and route choice considerations. The proposed model is formulated as a variational inequality problem and solved via a route-based algorithm using the modified alternating direction method. Numerical analyses are also provided to illustrate the features of the proposed model and the applicability of the solution algorithm.

Journal of Advanced Transportation, 2008

Recent empirical studies on the value of time and reliability reveal that travel time variability... more Recent empirical studies on the value of time and reliability reveal that travel time variability plays an important role on travelers' route choice decision process. It can be considered as a risk to travelers making a trip. Therefore, travelers are not only interested in saving their travel time but also in reducing their risk. Typically, risk can be represented by two different aspects: acceptable risk and unacceptable risk. Acceptable risk refers to the reliability aspect of acceptable travel time, which is defined as the average travel time plus the acceptable additional time (or buffer time) needed to ensure more frequent on-time arrivals, while unacceptable risk refers to the unreliability aspect of unacceptable late arrivals (though infrequent) that have a travel time excessively higher than the acceptable travel time. Most research in the network equilibrium based approach to modeling travel time variability ignores the unreliability aspect of unacceptable late arrivals. This paper examines the effects of both reliability and unreliability aspects in a network equilibrium framework. Specifically, the traditional user equilibrium model, the demand driven travel time reliability-based user equilibrium model, and the α-reliable mean-excess travel time user equilibrium model are considered in the investigation under an uncertain environment due to stochastic travel demand. Numerical results are presented to examine how these models handle risk under travel time variability.