Browsing by Author "Wong, S. C."

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AN ESTIMATION OF EFFICIENT TIME-VARYING TOLLS FOR CROSS HARBOR TUNNELS IN HONG KONG
(2011-12-01)
Hau, Timothy D.
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Loo, Becky P. Y.
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Wong, K. I.
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Wong, S. C.
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運輸與物流管理系註：原交通所+運管所
This work estimates the distribution of a time-varying toll over a 24-hour period that minimizes the combined queue length of the three tunnels that traverse Hong Kong's Victoria Harbour, taking into account institutional constraints. Our results reveal that switching from a flat toll to a time-varying toll scheme would eliminate all existing tunnel queues. We argue that optimal tunnel tolling, coupled with the nonstop electronic toll collection mechanism already in place, could be the first step toward the implementation of electronic road pricing in Hong Kong. Optimal tolling would obviate the need to build a fourth harbor crossing in the near future.
Modeling urban taxi services with multiple user classes and vehicle modes
(2008-12-01)
Wong, K. I.
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Wong, S. C.
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Yang, Hai
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Wu, J. H.
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運輸與物流管理系註：原交通所+運管所
This paper extends the model of urban taxi services in congested networks to the case of multiple user classes, multiple taxi modes, and customer hierarchical modal choice. There are several classes of customers with different values of time and money, and several modes of taxi services with distinct combinations of service area restrictions and fare levels. The multi-class multi-mode formulation allows the modeling of both mileage-based and congestion-based taxi fare charging mechanisms in a unified framework, and can more realistically model most urban taxi services, which are charged on the basis of both time and distance. The introduction of multiple taxi modes can also be used to model the differentiation between luxury taxis and normal taxis by their respective service areas and customer waiting times. We propose a simultaneous mathematical formulation of two equilibrium sub-problems for the model. One sub-problem is a combined network equilibrium model (CNEM) that describes the hierarchical logit mode choice model of occupied taxis and normal traffic, together with the vacant taxi distributions in the network. The other sub-problem is a set of linear and nonlinear equations (SLNE), which ensures the satisfaction of the relation between taxi and customer waiting times, the relation between customer demand and taxi supply for each taxi mode, and taxi service time constraints. The CNEM can be formulated as a variational inequality program that is solvable by means of a block Gauss-Seidel decomposition approach coupled with the method of successive averages. The SLNE can be solved by a Newtonian algorithm with a line search. The CNEM is formulated as a special case of the general travel demand model so that it is possible to incorporate the taxi model into an existing package as an add-on module, in which the algorithm for the CNEM is built in practice. Most of the parameters are observable, given that such a calibrated transport planning model exists. A numerical example is used to demonstrate the effectiveness of the proposed methodology. (C) 2008 Elsevier Ltd. All rights reserved.
Nonlinear pricing of taxi services
(2010-06-01)
Yang, Hai
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Fung, C. S.
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Wong, K. I.
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Wong, S. C.
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運輸與物流管理系註：原交通所+運管所
This paper examines the effects of nonlinear fare structures in taxi markets using an extended taxi model with an explicit consideration of perceived profitability. The expected profit, defined as the profit per unit time (inclusive of both occupied and vacant taxi times), that a taxi driver expects to receive from picking up a customer in a particular zone or location, has great impact on the taxi driver's choice of location in the search for customers. The fare structure directly governs the profitability of taxi rides of different distances originating from different locations. With these explicit considerations, the extended model is intended to look into the market effects of adopting a nonlinear fare structure with declining incremental charges. The proposed nonlinear fare structure could help restore a level-playing field for taxi operators whose businesses have been affected by some taxi drivers who resort to practices such as offering fare discounts or accepting requests for discounted fares from passengers for long-haul trips. Analysis of sensitivity of social welfare and profit gain as well as taxi/customer wait/search times is conducted with respect to the parameters in the nonlinear fare structure for the Hong Kong taxi market, and Pareto-improving nonlinear fare amendments are identified that neither disadvantage any customer nor reduce the taxi operators' profits. (C) 2010 Elsevier Ltd. All rights reserved.