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Personal rapid transit (PRT) is a kind of innovative public transport service operated by autonomous vehicles on a dedicated guideway network. In the situation, where PRT guideway network is composed of unidirectional links, the congestion degree of network and vehicle travel distance depend on the arrangement of link directions, given certain traffic demand and network configuration. The motivation of this paper is to propose a method to optimize the link direction of PRT network for enhancing system performance. The proposed optimization problem considers both the vehicle travel time and waiting time at merging nodes as the optimization objective and is formulated as a non-linear programming model. A linear approximation-based solution method is further developed to obtain solutions in an efficient way and the exact solution is achieved via this method. The result shows that the proposed method is effective to find an optimized arrangement of link directions in the network given certain travel demand and network configuration. The computational results of the proposed model in comparison to other models are presented and discussed, which show that the significant reduction of waiting time does not necessarily lead to the high increase of travel time, suggesting the importance of congestion control for merging modes. [ABSTRACT FROM AUTHOR]

Water supply systems around the world are becoming increasingly vulnerable as a consequence of rising climate instability and the systems' intrinsic complexity. Assessing the vulnerability of such systems is the primary and fundamental step for mitigating the negative impacts of environmental incidents. There are two main challenges in this context. First, since water supply systems are coupled with human-environment systems, the corresponding vulnerability assessment requires consideration of a host of multidimensional criteria in terms of the structures and management. Second, due to the uncertain and dynamic nature of environmental incidents, available information is not sufficient for experts to make accurate real-time judgments for the weights of criteria. To the best of our knowledge, few weight calculation approaches are able to deal with both uncertainties and subjectivities of experts' judgments under varied scenarios of the incident. These problems are solved by developing new assessment approaches consisting of four steps: 1) developing an analytical network process (ANP) criteria framework; 2) proposing a weight calculation approach by integrating game cross evaluation with stochastic ANP based on the proposed criteria framework; 3) calculating the weighted vulnerability values, rating and visualizing the vulnerability grades accordingly; and 4) performing assessment simulations and sensitivity analysis for possible scenarios. A case study of the Shanghai water supply system demonstrates the effectiveness of the proposed approaches, which provides guides for improvement of system performances based on the trends of variations in the vulnerability grades and the dominating criterion identified for each component. [ABSTRACT FROM AUTHOR]