共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
Ismail Chabini & Sridevi Ganugapati 《International Transactions in Operational Research》2002,9(3):279-302
The development of intelligent transportation systems (ITS) and the resulting need for the solution of a variety of dynamic traffic network models and management problems require faster‐than‐real‐time computation of shortest path problems in dynamic networks. Recently, a sequential algorithm was developed to compute shortest paths in discrete time dynamic networks from all nodes and all departure times to one destination node. The algorithm is known as algorithm DOT and has an optimal worst‐case running‐time complexity. This implies that no algorithm with a better worst‐case computational complexity can be discovered. Consequently, in order to derive algorithms to solve all‐to‐one shortest path problems in dynamic networks, one would need to explore avenues other than the design of sequential solution algorithms only. The use of commercially‐available high‐performance computing platforms to develop parallel implementations of sequential algorithms is an example of such avenue. This paper reports on the design, implementation, and computational testing of parallel dynamic shortest path algorithms. We develop two shared‐memory and two message‐passing dynamic shortest path algorithm implementations, which are derived from algorithm DOT using the following parallelization strategies: decomposition by destination and decomposition by transportation network topology. The algorithms are coded using two types of parallel computing environments: a message‐passing environment based on the parallel virtual machine (PVM) library and a multi‐threading environment based on the SUN Microsystems Multi‐Threads (MT) library. We also develop a time‐based parallel version of algorithm DOT for the case of minimum time paths in FIFO networks, and a theoretical parallelization of algorithm DOT on an ‘ideal’ theoretical parallel machine. Performances of the implementations are analyzed and evaluated using large transportation networks, and two types of parallel computing platforms: a distributed network of Unix workstations and a SUN shared‐memory machine containing eight processors. Satisfactory speed‐ups in the running time of sequential algorithms are achieved, in particular for shared‐memory machines. Numerical results indicate that shared‐memory computers constitute the most appropriate type of parallel computing platforms for the computation of dynamic shortest paths for real‐time ITS applications. 相似文献
3.
传统Dijkstra算法在路径规划时无法适用于具有交通规则约束的交通网络。为解决该问题,在以往的路网模型和算法的基础上,提出一种具有交通规则约束的改进Dijkstra算法。算法对节点新增"待选择状态"和"可再更新状态",用以解决节点具有交通规则约束的问题;同时引入祖父节点,从而生成交通网络中各节点的三元组信息,以此作为回溯依据,可以得到从初始节点到目的节点的最短路径。该算法不仅适用于具有交通规则约束的交通网络,且具有较低的复杂度。通过理论分析证明了算法的正确性,并以长春市朝阳区的实际交通网络和随机添加的交通规则约束为数据进行了实验测试,验证了算法的有效性。 相似文献
4.
5.
6.
7.
8.
9.
10.
智能交通信息物理融合云控制系统 总被引:12,自引:5,他引:7
针对现代智能交通信息物理融合路网建设中的对象种类复杂、采集数据量大、传输及计算需求高以及实时调度控制能力弱等问题,基于云控制系统理论,以现代智能交通控制网络为研究对象,设计了智能交通信息物理融合云控制系统方案,包括智能交通边缘控制技术和智能交通网络虚拟化技术.基于智能交通流大数据,在云控制管理中心服务器上利用深度学习和超限学习机等智能学习方法对采集的交通流数据进行训练预测计算,能够预测城市道路的短时交通流和拥堵状况.进一步在云端利用智能优化调度算法得到实时的交通流调控策略,用于解决拥堵路段交通流分配难题,提高智能交通控制系统动态运行性能.仿真结果表明了本文方法的有效性. 相似文献
11.
In this study, a traffic management measure is presented by combining the route guidance of Advanced Traveler Information System (ATIS) and the continuous network design (CNDP) to alleviate increasing traffic congestion. The route guidance recommends the travelers to choose the shortest path based on marginal travel cost and user constraints. The problem is formulated into a bi-level programming problem. The most distinct property of this problem formulation is that the feasible path set of its lower-level problem is determined by the decision variable of upper-level problem, while in conventional transportation network design problems the feasible path set for lower-level traffic assignment problem is fixed to be all the viable paths between each specific origin-destination pair. The simulated annealing algorithm is improved to solve this bi-level problem. A path-based traffic algorithm is developed to calculate the lower-level traffic assignment problem under the route guidance. Compared to the results of conventional CNDP, the measure presented in this study can better improve the transportation network performance. 相似文献
12.
13.
基于城市道路网的最短路径分析解决方案 总被引:23,自引:0,他引:23
近年来GIS对网络分析功能的需求迅速增长.网络分析中的一个关键问题是最短路径问题,它作为许多领域中速择最优问题的基础,在交通网络分析系统中占有重要地位.由于最短路径分析常用于汽车导航系统以及各种城市应急系统(如l10报警、l19火警以及120急救系统),本文针对城市道路网的特点,提出了一种实用、高效的最短路径分析解决方案. 相似文献
14.
Routing in a stochastic and dynamic (time-dependent) network is a crucial transportation problem. A new variant of adaptive routing, which assumes perfect online information of continuous real-time link travel time, is proposed. Driver's speed profile is taken into consideration to realistically estimate travel times, which also involves the stochasticity of links in a dynamic network. An adaptive approach is suggested to tackle the continuous dynamic shortest path problem. A decremental algorithm is consequently developed to reduce optimization time. The impact of the proposed adaptive routing and the performance of the decremental approach are evaluated in static and dynamic networks under different traffic conditions. The proposed approach can be incorporated into vehicle navigation systems. 相似文献
15.
16.
基于改进蚁群算法的最短路径问题研究 总被引:4,自引:0,他引:4
最短路径问题是智能交通:交通网络分析中的一个重要问题。文章分析了基本蚁群算法在求解交通网络两点之间最短路径时所出现的问题,并针对这些问题,在方向引导及信息素更新等方面对算法进行了改进。实验证明,改进后的方法较基本蚁群算法能准确快速地找到交通路网中两点间的最短路径,是切实可行的。 相似文献
17.
18.
针对车辆在通过无信号灯交叉路口时存在等待时间长、通行效率低等问题,提出了一种基于增强型Dijkstra算法的优化调度方案。以智能车辆为研究对象,在将交叉路口网格化的基础上,综合考虑车辆在每个网格中的方向权值、安全权值和优先级权值,制定了动态网格权值赋值原则,进而搜索通行时间最短的路径。相比Dijkstra算法,提出的增强型Dijkstra算法实现了智能车辆在动态网格权值下最短路径的全局搜索,可以根据实际车辆环境灵活调整每个车辆的行驶轨迹。仿真结果表明,增强型Dijkstra算法不仅能够保持较低的冲突次数,还能有效减少车辆总通行时间。在100 m×100 m的双向六车道的交叉路口环境下,车辆平均停车延误减少1.5 s,冲突率下降13%。 相似文献
19.
20.
公交车网络的最短路径算法及实现 总被引:3,自引:0,他引:3
最短路径问题是图论研究中的一个经典算法问题.旨在寻找图中任意两结点之间的最短路径。一般在交通道路网络中最短路径问题就是单纯地求解两点问的最短路径。为了保证实用性,公交车网络的最短路径算法以转车次数最少为首要目的。文中借鉴广度优先搜索的思路来求解最短路径,即逐个找出经过起点站和终点站的车次以及这些车次沿途可转的车次。首先说明了算法的计算机实现方法,再举例详细说明其过程,最后指出此算法的扩充用途。 相似文献