Seungkyu Ryu - Academia.edu (original) (raw)

Papers by Seungkyu Ryu

Research paper thumbnail of Path flow estimator for planning applications in small communities

Research paper thumbnail of Investigating Travel Time Reliability Measures in Toll Design Problem

Research paper thumbnail of Modeling Demand Elasticity and Route Overlapping in Stochastic User Equilibrium Through Paired Combinatorial Logit Model

Research paper thumbnail of A modified gradient projection algorithm for solving the elastic demand traffic assignment problem

This paper develops a path-based traffic assignment algorithm for solving the elastic demand traf... more This paper develops a path-based traffic assignment algorithm for solving the elastic demand traffic assignment problem (EDTAP). A modified path-based gradient projection (GP) method combined with a column generation is suggested for solving the equivalent excess-demand reformulation of the problem in which the elastic demand problem is reformulated as a fixed demand problem through an appropriate modification of network representation. Numerical results using a set of real transportation networks are provided to demonstrate the efficiency of the modified GP algorithm for solving the excess-demand formulation of the EDTAP. In addition, a sensitivity analysis is conducted to examine the effects of the scaling parameter used in the elastic demand function on the estimated total demand, number of generated paths, number of used paths, and computational efforts of the modified GP algorithm.

Research paper thumbnail of Modeling mode and route similarities in network equilibrium problem with go-green modes

Research paper thumbnail of L-infinity norm for handling traffic count inconsistencies in path flow estimator: formulation and solution algorithm

Research paper thumbnail of A Two-Stage Approach for Estimating a Statewide Truck Trip Table

Research paper thumbnail of AN EVALUATION FRAMEWORK OF AUTOMATED ELECTRIC TRANSPORTATION SYSTEM

Research paper thumbnail of A Dual Approach for Solving the Combined Distribution and Assignment Problem with Link Capacity Constraints

Networks and Spatial Economics, 2014

In this paper, we consider the combined distribution and assignment (CDA) problem with link capac... more In this paper, we consider the combined distribution and assignment (CDA) problem with link capacity constraints modeled as a hierarchical logit choice problem based on random utility theory. The destination and route choices are calculated based on the multi-nominal logit probability function, which forms the basis for constructing the side constrained CDA (SC-CDA) problem as an equivalent mathematical programming (MP) formulation. A dual MP formulation of the SC-CDA problem is developed as a solution algorithm, which consists of an iterative balancing scheme and a column generation scheme, for solving the SC-CDA problem. Due to the entropy-type objective function, the dual formulation has a simple nonlinear constrained optimization structure, where the feasible set only consists of nonnegative orthants. The iterative balancing scheme explicitly makes use of the optimality conditions of the dual formulation to analytically adjust the dual variables and update the primal variables, while a column generation scheme is used to iteratively generate routes to the working route set as needed to satisfy the side constraints. Two numerical experiments are conducted to demonstrate the features of the SC-CDA model and the computational performance of the solution algorithm. The results reveal that imposing link capacity constraints can have a significant impact on the network equilibrium flow allocations, and the dual approach is a practical solution algorithm for solving the complex SC-CDA problem.

Research paper thumbnail of Norm Path Flow Estimator for Handling Traffic Count Inconsistencies: Formulation and Solution Algorithm

Journal of Transportation Engineering, 2010

Path flow estimator ͑PFE͒ is a single-level network observer proposed to estimate path flows and ... more Path flow estimator ͑PFE͒ is a single-level network observer proposed to estimate path flows and origin-destination flows from traffic counts in a transportation network. The PFE model handles the traffic count inconsistency problem by allowing user to specify appropriate error bounds ͑or confidence interval͒ on the traffic counts. This approach, although flexible, introduces a systematic bias in underestimating the total demand when improper error bounds are specified. This paper presents an L ϱ -norm PFE model that minimizes the systematic bias of the total demand estimate encountered in the PFE model by determining the least maximum absolute error needed to accommodate measurement errors and traffic count inconsistencies within the estimation process. A solution algorithm based on the dual formulation combined with a column generation procedure is developed for solving the proposed L ϱ -norm PFE model. Numerical results are presented to illustrate the features and applicability of the proposed L ϱ -norm PFE model and solution algorithm.

Research paper thumbnail of Computation and application of the paired combinatorial logit stochastic user equilibrium problem

Computers & Operations Research, 2014

Research paper thumbnail of Bus rapid transit operation analysis using the Downs–Thomson paradox

The purpose of the paper is to analyze effectiveness before and after implementation of the bus r... more The purpose of the paper is to analyze effectiveness before and after implementation of the bus rapid transit operation. The paper includes a speed analysis based on the Downs-Thomson paradox, and a reliability analysis based on variance analysis of arrival time. According to the speed analysis, some road sections are now under phase 2 in the Downs-Thomson paradox, which is a state in which the bus speeds are greater than the auto speeds. In the future, it is predicted that autos and buses will reach an equilibrium speed which is in phase 3 of the multi-modal equilibrium theory. According to the reliability analysis of arrival time at each bus stop, in roads of median arterial bus lanes, the variance of arrival time is generally smaller than after the scheme implemented in 8 months later.

Research paper thumbnail of Multiple path-finding models using Kalman filtering and space syntax techniques

ABSTRACT A study was done to develop a shortest path algorithm in which the realism of way findin... more ABSTRACT A study was done to develop a shortest path algorithm in which the realism of way finding had been improved by incorporating the concept of road cognition. The existing shortest path algorithms consider travel time and travel distance only. However, cognition of road configurations also can be considered for providing a realistically satisfied path. Surveys have shown that people prefer a high-cognition path rather than a low-cognition path. Therefore, the study developed a shortest path algorithm to provide a realistically plausible route that is preferred by many people and that considered the travel time, travel distance, and road cognition. The profiles of travel times, which are required to estimate arrival times up to destination, are predicted by using a Kalman filtering technique to reflect time-varying travel conditions. The travel distance is calculated by using the geographic information system (GIS) attributes, and road cognition is established by applying a space syntax technique to identify road configurations. Also, space data of the space syntax model are based on GIS data. By considering both the shortest path in terms of travel time and distance and the best cognition in terms of road configurations, multiple paths are determined.

Research paper thumbnail of L-Infinity Norm Model for Handling Traffic Count Inconsistencies in Path Flow Estimator

Research paper thumbnail of Alpha reliable network design problem: efficiency versus equity

Research paper thumbnail of Examining the scaling effect and overlapping problem in logit-based stochastic user equilibrium models

Research paper thumbnail of Quality Measures of Origin-Destination Trip Table Estimated from Traffic Counts: Review and New Generalized Demand Scale Measure

Research paper thumbnail of Alternative Planning Tool for Small Metropolitan Planning Organization in Utah

Research paper thumbnail of An intersection turning movement estimation procedure based on path flow estimator

Estimation of intersection turning movements is one of the key inputs required for a variety of t... more Estimation of intersection turning movements is one of the key inputs required for a variety of transportation analysis, including intersection geometric design, signal timing design, traffic impact assessment, and transportation planning. Conventional approaches that use manual techniques for estimation of turning movements are insensitive to congestion. The drawbacks of the manual techniques can be amended by integrating a network traffic model with a computation procedure capable of estimating turning movements from a set of link traffic counts and intersection turning movement counts. This study proposes using the path flow estimator, originally used to estimate path flows (hence origin-destination flows), to derive not only complete link flows, but also turning movements for the whole road network given some counts at selected roads and intersections. Two case studies using actual traffic counts are used to demonstrate the proposed intersection turning movement estimation procedure.

Research paper thumbnail of A self-adaptive Armijo stepsize strategy with application to traffic assignment models and algorithms

Stepsize determination is an important component of algorithms for solving several mathematical f... more Stepsize determination is an important component of algorithms for solving several mathematical formulations. In this article, a self-adaptive Armijo strategy is proposed to determine an acceptable stepsize in a more efficient manner. Instead of using a fixed initial stepsize in the original Armijo strategy, the proposed strategy allows the starting stepsize per iteration to be self-adaptive. Both the starting stepsize

Research paper thumbnail of Path flow estimator for planning applications in small communities

Research paper thumbnail of Investigating Travel Time Reliability Measures in Toll Design Problem

Research paper thumbnail of Modeling Demand Elasticity and Route Overlapping in Stochastic User Equilibrium Through Paired Combinatorial Logit Model

Research paper thumbnail of A modified gradient projection algorithm for solving the elastic demand traffic assignment problem

This paper develops a path-based traffic assignment algorithm for solving the elastic demand traf... more This paper develops a path-based traffic assignment algorithm for solving the elastic demand traffic assignment problem (EDTAP). A modified path-based gradient projection (GP) method combined with a column generation is suggested for solving the equivalent excess-demand reformulation of the problem in which the elastic demand problem is reformulated as a fixed demand problem through an appropriate modification of network representation. Numerical results using a set of real transportation networks are provided to demonstrate the efficiency of the modified GP algorithm for solving the excess-demand formulation of the EDTAP. In addition, a sensitivity analysis is conducted to examine the effects of the scaling parameter used in the elastic demand function on the estimated total demand, number of generated paths, number of used paths, and computational efforts of the modified GP algorithm.

Research paper thumbnail of Modeling mode and route similarities in network equilibrium problem with go-green modes

Research paper thumbnail of L-infinity norm for handling traffic count inconsistencies in path flow estimator: formulation and solution algorithm

Research paper thumbnail of A Two-Stage Approach for Estimating a Statewide Truck Trip Table

Research paper thumbnail of AN EVALUATION FRAMEWORK OF AUTOMATED ELECTRIC TRANSPORTATION SYSTEM

Research paper thumbnail of A Dual Approach for Solving the Combined Distribution and Assignment Problem with Link Capacity Constraints

Networks and Spatial Economics, 2014

In this paper, we consider the combined distribution and assignment (CDA) problem with link capac... more In this paper, we consider the combined distribution and assignment (CDA) problem with link capacity constraints modeled as a hierarchical logit choice problem based on random utility theory. The destination and route choices are calculated based on the multi-nominal logit probability function, which forms the basis for constructing the side constrained CDA (SC-CDA) problem as an equivalent mathematical programming (MP) formulation. A dual MP formulation of the SC-CDA problem is developed as a solution algorithm, which consists of an iterative balancing scheme and a column generation scheme, for solving the SC-CDA problem. Due to the entropy-type objective function, the dual formulation has a simple nonlinear constrained optimization structure, where the feasible set only consists of nonnegative orthants. The iterative balancing scheme explicitly makes use of the optimality conditions of the dual formulation to analytically adjust the dual variables and update the primal variables, while a column generation scheme is used to iteratively generate routes to the working route set as needed to satisfy the side constraints. Two numerical experiments are conducted to demonstrate the features of the SC-CDA model and the computational performance of the solution algorithm. The results reveal that imposing link capacity constraints can have a significant impact on the network equilibrium flow allocations, and the dual approach is a practical solution algorithm for solving the complex SC-CDA problem.

Research paper thumbnail of Norm Path Flow Estimator for Handling Traffic Count Inconsistencies: Formulation and Solution Algorithm

Journal of Transportation Engineering, 2010

Path flow estimator ͑PFE͒ is a single-level network observer proposed to estimate path flows and ... more Path flow estimator ͑PFE͒ is a single-level network observer proposed to estimate path flows and origin-destination flows from traffic counts in a transportation network. The PFE model handles the traffic count inconsistency problem by allowing user to specify appropriate error bounds ͑or confidence interval͒ on the traffic counts. This approach, although flexible, introduces a systematic bias in underestimating the total demand when improper error bounds are specified. This paper presents an L ϱ -norm PFE model that minimizes the systematic bias of the total demand estimate encountered in the PFE model by determining the least maximum absolute error needed to accommodate measurement errors and traffic count inconsistencies within the estimation process. A solution algorithm based on the dual formulation combined with a column generation procedure is developed for solving the proposed L ϱ -norm PFE model. Numerical results are presented to illustrate the features and applicability of the proposed L ϱ -norm PFE model and solution algorithm.

Research paper thumbnail of Computation and application of the paired combinatorial logit stochastic user equilibrium problem

Computers & Operations Research, 2014

Research paper thumbnail of Bus rapid transit operation analysis using the Downs–Thomson paradox

The purpose of the paper is to analyze effectiveness before and after implementation of the bus r... more The purpose of the paper is to analyze effectiveness before and after implementation of the bus rapid transit operation. The paper includes a speed analysis based on the Downs-Thomson paradox, and a reliability analysis based on variance analysis of arrival time. According to the speed analysis, some road sections are now under phase 2 in the Downs-Thomson paradox, which is a state in which the bus speeds are greater than the auto speeds. In the future, it is predicted that autos and buses will reach an equilibrium speed which is in phase 3 of the multi-modal equilibrium theory. According to the reliability analysis of arrival time at each bus stop, in roads of median arterial bus lanes, the variance of arrival time is generally smaller than after the scheme implemented in 8 months later.

Research paper thumbnail of Multiple path-finding models using Kalman filtering and space syntax techniques

ABSTRACT A study was done to develop a shortest path algorithm in which the realism of way findin... more ABSTRACT A study was done to develop a shortest path algorithm in which the realism of way finding had been improved by incorporating the concept of road cognition. The existing shortest path algorithms consider travel time and travel distance only. However, cognition of road configurations also can be considered for providing a realistically satisfied path. Surveys have shown that people prefer a high-cognition path rather than a low-cognition path. Therefore, the study developed a shortest path algorithm to provide a realistically plausible route that is preferred by many people and that considered the travel time, travel distance, and road cognition. The profiles of travel times, which are required to estimate arrival times up to destination, are predicted by using a Kalman filtering technique to reflect time-varying travel conditions. The travel distance is calculated by using the geographic information system (GIS) attributes, and road cognition is established by applying a space syntax technique to identify road configurations. Also, space data of the space syntax model are based on GIS data. By considering both the shortest path in terms of travel time and distance and the best cognition in terms of road configurations, multiple paths are determined.

Research paper thumbnail of L-Infinity Norm Model for Handling Traffic Count Inconsistencies in Path Flow Estimator

Research paper thumbnail of Alpha reliable network design problem: efficiency versus equity

Research paper thumbnail of Examining the scaling effect and overlapping problem in logit-based stochastic user equilibrium models

Research paper thumbnail of Quality Measures of Origin-Destination Trip Table Estimated from Traffic Counts: Review and New Generalized Demand Scale Measure

Research paper thumbnail of Alternative Planning Tool for Small Metropolitan Planning Organization in Utah

Research paper thumbnail of An intersection turning movement estimation procedure based on path flow estimator

Estimation of intersection turning movements is one of the key inputs required for a variety of t... more Estimation of intersection turning movements is one of the key inputs required for a variety of transportation analysis, including intersection geometric design, signal timing design, traffic impact assessment, and transportation planning. Conventional approaches that use manual techniques for estimation of turning movements are insensitive to congestion. The drawbacks of the manual techniques can be amended by integrating a network traffic model with a computation procedure capable of estimating turning movements from a set of link traffic counts and intersection turning movement counts. This study proposes using the path flow estimator, originally used to estimate path flows (hence origin-destination flows), to derive not only complete link flows, but also turning movements for the whole road network given some counts at selected roads and intersections. Two case studies using actual traffic counts are used to demonstrate the proposed intersection turning movement estimation procedure.

Research paper thumbnail of A self-adaptive Armijo stepsize strategy with application to traffic assignment models and algorithms

Stepsize determination is an important component of algorithms for solving several mathematical f... more Stepsize determination is an important component of algorithms for solving several mathematical formulations. In this article, a self-adaptive Armijo strategy is proposed to determine an acceptable stepsize in a more efficient manner. Instead of using a fixed initial stepsize in the original Armijo strategy, the proposed strategy allows the starting stepsize per iteration to be self-adaptive. Both the starting stepsize