Browsing by Author "Chen, Hui-Ju"

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A Bilevel Model With a Solution Algorithm for Locating Weigh-In-Motion Stations
(2018-02-01)
Lu, Chung-Cheng
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Yan, Shangyao
;
Ko, Hao-Chih
;
Chen, Hui-Ju
;
運輸與物流管理系註：原交通所+運管所
The proper location of weigh-in-motion (WIM) stations in road networks is critical to effectively reduce the impact of overweight trucks. Truckers may quickly learn the locations of WIM stations, and take detours to bypass these checkpoints, with the aid of advanced navigation systems. This reaction needs to he considered in the location models for the deployment of WIM systems. This paper proposes a bilevel model to deal with the WIM location problem in a road network. The model includes an upper level and multiple lower level models respectively, represent the decision-making behavior of the law enforcement officials and truckers for different origin?destination pairs. The upper level model determines the optimal number and locations of WIM stations so as to minimize the damage due to evasive overweight trucks, considering the truckers' route choices. The lower level models simulate the truckers' route choices in response to the WIM locations determined by the upper level model. A heuristic is developed to efficiently solve the bilevel model, as it is difficult to obtain the exact solution. The proposed model and heuristic are evaluated using a test instance generated based on the Nevada road network. The results show that the heuristic outperforms a classical approach based on k shortest paths.
Optimal Allocation of Cashiers and Pharmacists in Large Hospitals: A Point-Wise Fluid-Based Dynamic Queueing Network Approach
(2018-01-01)
Lu, Chung-Cheng
;
Lin, Shih-Wei
;
Chen, Hui-Ju
;
Ying, Kuo-Ching
;
運輸與物流管理系註：原交通所+運管所
This paper presents an optimization model for determining the optimal time-varying numbers of cashiers and pharmacists in a large hospital. The objective of this model is to minimize the weighted sum of the waiting cost incurred by patients and the operating costs incurred by the hospital. A point-wise fluid based approximation approach is adopted to construct a dynamic queuing network that takes into account time-varying (or non-stationary) arrivals of patients and describes time-varying queue lengths. The dynamic queuing network is then encapsulated in the optimization model that determines the optimal time-varying numbers of cashiers and pharmacists. A test problem instance is designed based on a large hospital in the city of Taipei, and the MINOS solver of GAMS is applied to solve the problem instance. Sensitivity analyses are also conducted to examine the impacts of customer arrival rates and service rates on the waiting cost and operational cost. Numerical results show that the optimization model can provide an optimal allocation of manpower that significantly reduces both waiting and operating costs.