Showing papers by "Zhiyuan Liu published in 2013"

Bus stop-skipping scheme with random travel time

Abstract: When a bus is late and behind schedule, the stop-skipping scheme allows the bus vehicle to skip one or more stops to reduce its travel time. The deadheading problem is a special case of the stop-skipping problem, allowing a bus vehicle to skip stops between the dispatching terminal point and a designated stop. At the planning level, the optimal operating plans for these two schemes should be tackled for the benefits of bus operator as well as passengers. This paper aims to propose a methodology for this objective. Thus, three objectives are first proposed to reflect the benefits of bus operator and/or passengers, including minimizing the total waiting time, total in-vehicle travel time and total operating cost. Then, assuming random bus travel time, the stop-skipping is formulated as an optimization model minimizing the weighted sum of the three objectives. The deadheading problem can be formulated via the same minimization model further adding several new constraints. Then, a Genetic Algorithm Incorporating Monte Carlo Simulation is proposed to solve the optimization model. As validated by a numerical example, the proposed algorithm can obtain a satisfactory solution close to the global optimum.

Bunker consumption optimization methods in shipping: A critical review and extensions

Abstract: It is crucial nowadays for shipping companies to reduce bunker consumption while maintaining a certain level of shipping service in view of the high bunker price and concerned shipping emissions. After introducing the three bunker consumption optimization contexts: minimization of total operating cost, minimization of emission and collaborative mechanisms between port operators and shipping companies, this paper presents a critical and timely literature review on mathematical solution methods for bunker consumption optimization problems. Several novel bunker consumption optimization methods are subsequently proposed. The applicability, optimality, and efficiency of the existing and newly proposed methods are also analyzed. This paper provides technical guidelines and insights for researchers and practitioners dealing with the bunker consumption issues.

Speed-based toll design for cordon-based congestion pricing scheme

Abstract: The cordon-based Electronic Road Pricing (ERP) system in Singapore adopts the average travel speed as an index for evaluating the traffic congestion within a cordon area, and the maintenance of the average travel speed within a satisfactory range is taken as the objective of the toll adjustment. To formulate this practical speed-based toll design problem, this paper proposes a mathematical programming with equilibrium constraint (MPEC) model with the objective of maintaining the traffic condition in the cordon area. In the model, the network users’ route choice behavior is assumed to follow probit-based stochastic user equilibrium with elastic demand, asymmetric link travel time functions and continuous value-of-time. A distributed revised genetic algorithm is designed for solving the MPEC model. Finally, a network example based on the ERP system is adopted to numerically validate the proposed models and algorithms, and further indicates that the computation speed can be improved greatly by using a distributed computing system.

Robust optimization model of bus transit network design with stochastic travel time

Abstract: The design of urban bus transit systems aims to determine a network configuration with a set of bus lines and associated frequencies that achieve the targeted objective. This paper presents a methodology framework to formulate and solve the bus transit network design problem (TNDP). It first proposes a TNDP taking into account the travel time stochasticity. A robust optimization model is formulated for the proposed problem, which aims to minimize the sum of the expected value of the operator cost and its variability multiplied by a weighting value. A heuristic solution approach, based on k-shortest path algorithm, simulated annealing algorithm, Monte Carlo simulation, and probit-type discrete choice model, is subsequently developed to solve the robust optimization model. Finally, the proposed methodology is applied to a numerical example. (C) 2013 American Society of Civil Engineers.

Containership scheduling with transit-time-sensitive container shipment demand

Abstract: This paper examines the optimal containership schedule with transit-time-sensitive demand that is assumed to be a decreasing continuous function of transit time. A mixed-integer nonlinear non-convex optimization model is first formulated to maximize the total profit of a ship route. In view of the problem structure, a branch-and-bound based holistic solution method is developed. It is rigorously demonstrated that this solution method can obtain an e-optimal solution in a finite number of iterations for general forms of transit-time-sensitive demand. Computational results based on a trans-Pacific liner ship route demonstrate the applicability and efficiency of the solution method.

A Note on "Berth Allocation Considering Fuel Consumption and Vessel Emissions"

Abstract: Du et al. [Du, Y., Chen, Q., Quan, X., Long, L., Fung, R.Y.K., 2011. Berth allocation considering fuel consumption and vessel emissions. Transportation Research Part E 47, 1021–1037] dealt with a berth allocation problem incorporating ship’ fuel consumption minimization. To address the difficulty posed by the power function between fuel consumption rate and sailing speed, they formulated a tractable mixed-integer second-order cone programming model. We propose two quadratic outer approximation approaches that can handle general fuel consumption rate functions more efficiently. In the static quadratic outer approximation approach, the approximation lines are generated a priori. In the dynamic quadratic outer approximation approach, the approximation lines are generated dynamically. Numerical experiments demonstrate the advantages of the two approaches.

Calibration of Platoon Dispersion Parameter Considering the Impact of the Number of Lanes

Abstract: Microscopic vehicle behaviors, such as car following, overtaking, and lane changing, may occur differently on links with different numbers of lanes. Thus, this paper addresses the impact of the number of lanes on the platoon dispersion of traffic flow in low-friction conditions. A well-adopted dispersion model is used to reflect the platoon dispersion. The platoon dispersion factor of the model is then recalibrated using data on road segments with different numbers of lanes. The data are obtained from a comprehensive survey taken at several locations on the arterial streets of Changchun and Hangzhou city, China, where each direction of road segment has two, three, four, or five lanes. The statistical results verify that the number of lanes does have an evident effect on the platoon dispersion factor α: when the number of lanes grows from two to five, the value of α decreases significantly; meanwhile, the slope of the function curve between α and the normalized flow becomes larger.

Fundamental properties of volume–capacity ratio of a private toll road in general networks

Abstract: It has been addressed in the existing literature that the volume–capacity (v/c) ratio on a private toll road is constant, regardless of the toll value and capacity set by the private companies for each toll road in the network. The previous derivation depends on the assumption that the user equilibrium flow on the private toll road is continuously differentiable with respect to its capacity and toll charge. In this paper, it is shown that the constant v/c ratio phenomenon still holds via relaxing this assumption. Such phenomenon is further examined in different scenarios: the v/c ratio remains constant under the demand regulation, markup charge regulation, and social cost minimization scheme; it may change under the rate-of-return regulation; it may decrease under capacity regulation and increase under the price-cap regulation. Moreover, this paper demonstrates that the v/c ratio may change if there are decreasing or increasing returns to scale in road construction, or the road capacity can only take discrete values, or link flow interactions are involved, whereas the v/c ratio remains constant in case of elastic demand.

An Overview on Multimodal Emergency Evacuation in an Urban Network

Abstract: Emergency evacuation is important following natural disasters, terrorist attacks or other causes. This can put an enormous amount of pressure on our transportation networks as the generated traffic demand can significantly exceed those for routine travel conditions. Applying the best attributes of each mode of transportation is thus vital in such scenarios. Depending on the nature of the hazard and the population characteristics within the threat area, the implementation of evacuation models and simulations has the potential to save a vast array of lives by providing an effective path to safety for inhabitants. This paper aims to present an overview of approaches to emergency evacuation in an urban network, their features and findings. Key findings show a deficit of research in models incorporating other modes such as pedestrians and public transit, synergising different evacuation strategies for efficient evacuation and realistic travel behaviour.

Transit Assignment Model Incorporating Bus Dwell Time

Abstract: The transit assignment problem with consideration of bus dwell time was analyzed in this study. The links in a transit network can be classified into four types: onboard, alighting, boarding, and dummy links. These types reflect bus dwelling behavior at bus stations. Accordingly, the travel time functions on these links can be analyzed. This paper proposes a new equation for the bus dwell time at each bus station; the dwell time is the maximum value between the passengers' boarding time and alighting time. An approach based on dynamic programming is used to describe the equilibrium passenger flow in the transit network. A gap function is proposed for formulating the equilibrium passenger flow, which can be solved with the revised optimal strategy algorithm and the method of successive averages. Two numerical examples in which the bus dwell time function is calibrated with real survey data are adopted. These examples validate the proposed methodology.

Systematic Network Design for Liner Shipping Services

Abstract: A systematic design for a liner shipping network was addressed. Many practical features in real-world operations, including multiple types of containers, container transshipment operations, empty container repositioning, origin-to-destination transit time constraints, consistent services with the current network, and joint services with other liner shipping companies, were considered. Given a set of candidate ship routes, some of these routes had to be used, and the use of others was optional. A mixed-integer linear programming model was proposed for the selection of optional ship routes. The solution of this model provided the laden and empty container flow on the selected ship routes. On the basis of the results of this model, techniques were proposed for refining ship routes by changing existing routes, designing new routes, and removing some routes. A large-scale numerical test based on the global shipping network of a liner shipping company, consisting of 166 ports, was performed.

On the weighting of the mean-absolute-deviation cost minimization model

Abstract: The mean-absolute-deviation cost minimization model, which aims to minimize sum of the mean value and the absolute deviation (AD) of the total cost multiplied by a given non-negative weighting, is one of a number of typical robust optimization models. This paper first uses a straightforward example to show that the solution obtained by this model with some weightings is not actually an optimal decision. This example also illustrates that the mean-absolute-deviation cost minimization model cannot be regarded as the conventional weighted transformation of the relevant multiobjective minimization model aiming to simultaneously minimize the mean value and AD. This paper further proves that the optimal solution obtained by the mean-absolute-deviation cost minimization model with the weighting not exceeding 0.5 will not be absolutely dominated by any other solution. This tight upper bound provides a useful guideline for practical applications.

A Dynamic Algorithm of Partitioning Urban Road Network into Traffic Control Subareas

Abstract: The objective of this study is to develop a dynamic algorithm for traffic control subarea partition. Influencing factors are classified into static factors and dynamic factors. We mainly focus on the three dynamic factors which are cycle length, platoon length and traffic flow continuation. An integrated correlation model is established to quantify the correlation degree of adjacent intersections and then a dynamic partition algorithm is developed based on the model. Both this algorithm and Changs algorithm, which is a representative achievement in subarea partition cited by Traffic control systems Handbook, are applied to a network including 20 signalized intersections in VISSIM to compare their benefits. Statistical results show that: (a) adjacent intersections with high correlation degree can be partitioned into one subarea to execute signal coordination according to our algorithm; (b) implementing our algorithm can save average vehicle delay by 8.9% and average vehicle stops by 7.8% than implementing Changs algorithm.

A Quick Offset Optimization Method for Traffic Signal Coordination

Abstract: To develop a quick offset optimization mehtod for traffic signal coordination scheme, the calculating methods for common cycle length and green split are brought forward firstly. Based on the vehicle delay model under isolated traffic control mode, the progression factor is introduced to improve the model. Then the relationship between progression factor and offset is derived. Minimizing average vehicle delay is selected as the optimization objective, the function with simple structure between the objective and offset is developed. At last, take two adjacent signalized intersections as example, the optimizaiton method is validated and the results show that the method is effective.

Suburban bus route design

Abstract: Rural and suburban areas have a low density of population. Hence, the bus services have unique features that enable the design of suburban bus route a practical and interesting research topic. We formulate a suburban bus route design problem and prove its NP-hardness. A dynamic programming approach is developed to obtain the optimal solution. A case study is reported to demonstrate the applicability of the proposed model and solution method.