基于地铁-货车联运的物流配送路径优化

为应对配送车辆引起道路拥堵和环境污染问题，提出地铁与货车联合运输. 在不改变地铁运行方案的前提下，利用地铁非高峰时段开展货物配送；考虑地铁剩余运能、货车容量、最大行驶距离、客户服务时间窗等限制条件，以配送距离最短为优化目标，构建基于地铁-货车联运的物流配送路径优化模型. 通过地铁配送路径设计不规则二维矩阵编码结构，使用改进自适应遗传算法求解. 以某市地铁货物运输为例，验证模型和算法的实用性、有效性. 结果表明，地铁-货车联合配送距离短，在客户时间窗范围内送达比例高，有效提高客户满意度.     

The value of real-time traffic information in urban freight distribution

Routes optimization in urban freight distribution is usually an off-line process based on the knowledge of historical conditions on the network. Real-time data provided by Intelligent Transportation Systems (ITSs) enable online re-optimization on the basis of actual traffic conditions.

?This paper evaluates the added value generated by re-optimizing the off-line solution with real-time information. The study is carried out for a practical application to the freight distribution of perishable goods in the city of Rome (Italy). The off-line problem is formulated as a vehicle routing problem with soft time windows while in the online problem it is also allowed to skip some customers or to re-sequence the deliveries. Both versions are solved with different algorithms and with different data sets. Results can be used to evaluate the potential return on investment on the acquisition of different kinds of traffic data. At the same time, results can be of interest for information providers, to fix the price of off-line and online information and/or to estimate the associated potential market share.     

STUDY ON NEIGHBORHOOD DISCOVERY PROTOCOL IN COMMUNICATION NETWORKS

IntroductionIt is well known thatthe PNNIsystem is a de-veloping system in the private ATM networkfield[1～ 5] .According to Ref.[6],PNNI includestwo categories of protocols,one defines for dis-tributing topology information between switchesand clusters of switches- routing protocol,and theother defines the signalling- signalling protocol,which is message flows used to establish point topoint and point to multi- point connections acrossthe ATM network.Forrealizing the PNNIroutingwith m…     

Weather impact on containership routing in closed seas: A chance-constraint optimization approach

Weather conditions have a strong effect on the operation of vessels and unavoidably influence total time at sea and associated transportation costs. The velocity and direction of the wind in particular may considerably affect travel speed of vessels and therefore the reliability of scheduled maritime services. This paper considers weather effects in containership routing; a stochastic model is developed for determining optimal routes for a homogeneous fleet performing pick-ups and deliveries of containers between a hub and several spoke ports, while incorporating travel time uncertainties attributed to the weather. The problem is originally formulated as a chance-constrained variant of the vehicle routing problem with simultaneous pick-ups and deliveries and time constraints and solved using a genetic algorithm. The model is implemented to a network of island ports of the Aegean Sea. Results on the application of algorithm reveal that a small fleet is sufficient enough to serve network’s islands, under the influence of minor delays. A sensitivity analysis based on alternative scenarios in the problem’s parameters, leads to encouraging conclusions with respect to the efficiency and robustness of the algorithm.     

A hybrid heuristic strategy for liquefied natural gas inventory routing

As liquefied natural gas (LNG) steadily grows to be a common mode for commercializing natural gas, LNG supply chain optimization is becoming a key technology for gas companies to maintain competitiveness. This paper develops methods for improving the solutions for a previously stated form of an LNG inventory routing problem (LNG-IRP). Motivated by the poor performance of a Dantzig-Wolfe-based decomposition approach for exact solutions, we develop a suite of advanced heuristic techniques and propose a hybrid heuristic strategy aiming to achieve improved solutions in shorter computational time. The heuristics include two phases: the advanced construction phase is based on a rolling time algorithm and a greedy randomized adaptive search procedure (GRASP); and the solution improvement phase is a series of novel MIP-based neighborhood search techniques. The proposed algorithms are evaluated based on a set of realistic large-scale instances seen in recent literature. Extensive computational results indicate that the hybrid heuristic strategy is able to obtain optimal or near optimal feasible solutions substantially faster than commercial optimization software and also the previously proposed heuristic methods.     

快速公交系统模式研究——以广州市BRT试验线系统为例

"快速通道+灵活线路"模式是城市快速公交应用中一种探索与创新的系统模式。以广州市BRT试验线为例介绍"快速通道+灵活线路"模式及其三个关键要素:快速专用通道、灵活线路运营、高效车站服务。探讨该模式在节省公交出行时间以及适应公共交通需求两方面的优势。分析"快速通道+灵活线路"模式的特性,并与传统的固定线路模式进行对比,归纳其三个关键要素与BRT系统效能的关系。最后,讨论了"快速通道+灵活线路"模式的适用条件,并指出快速公交的发展应走公交集约化和系统资源利用最大化的道路,提供快速、高效、便捷的高品质公共汽车交通服务。     

三峡库区定线制航路改革与航道条件探讨

介绍三峡库区航道的情况,对川江及三峡库区航行船舶的类型及航道条件进行了分析,得出:三峡库区实施定线制是可行的。对航道维护尺度进行了计算校核,目前航道维护尺度标准基本满足现有在川江航行船舶尺度要求。同时介绍了在三峡库区实施定线制航路改革后,由于部分航段未实施炸礁整治,目前汛期不能实现左右分边航行的原因,探讨了航标实行双侧连续配布后,航标等其他航道维护设施布设应注意的问题等。     

上海轨道交通2号线分段交路运营实践

上海轨道交通2号线实行分段交路、大小交路,运营管理非常复杂.在阐述2号线历史发展三个阶段的基础上,着重对目前分段交路交叉点车站(广兰路站)的行车组织和客运组织措施进行论述,最终得到2号线分段交路运营实践的经验总结:交叉点车站的行车组织是分段交路运营的重点.制定完备的正常作业规范和非正常运营下的应急处置预案,是确保两个交...     

基于层次拓扑的发布／订阅系统QoS路由策略研究

新型面向大规模的发布／订阅系统,能够使得信息交互的双方在时间、空间和控制流三个方面都被完全解耦。目前的对发布／订阅路由做了大量的研究,但是都没有提供一个通用的服务质量路由策略。设计了一个静态层次拓扑模型,在此基础上引入QoS保障策略,扩展了系统操作,提出了带QoS约束条件的路由算法的一般准则。     

Efficiency of routing and scheduling system for small and medium size enterprises utilizing vehicle location data

The routing and scheduling for trucks and vans in an urban road network depends critically on the state of the road network. Trucks and vans impose significant costs on other road users and the environment, so improved routing and scheduling benefits more than just the logistics industry. However, small and medium size enterprises (SMEs) in the logistics business cannot justify investment in planning systems. In this paper, an autonomous routing and scheduling system which is available to SMEs is proposed and the efficiency of the system is investigated. The proposed system accumulates vehicle location data in a central server and uses it to generate traffic information. Test simulations using a grid network demonstrate the effects of utilizing and sharing vehicle location data on delivery efficiency. The simulation results show that the improvement of delivery efficiency is mainly due to the reduction of penalty cost for early and late arrival at the customer location. It is also shown that the system leads to the buffer effect from variations in traffic conditions on delivery cost and this effect is enhanced by taking travel time uncertainty into consideration. It is further shown that the presence of measurement periods with insufficient data results in unreliable routing and scheduling. For a reliable system, data collection over a wider area is required rather than dense data in a subset of links.