【作者】 陈晨；

【导师】 陈建桥；

【作者基本信息】 华中科技大学 ， 固体力学， 2010， 博士

【摘要】 交通运输在国民经济和社会发展中起着举足轻重的作用,是国民经济的命脉。良好的交通运输系统是保障人们日常生活及加快经济发展的必须条件。先进的道路运输系统以及现代化的交通管理方法,是检验城市建设是否现代化的重要标准。随着我国经济建设的不断进步,人们对公路交通的需求逐渐增加。自从我国改革开放以来,落后的道路交通规划及管理带来的严重负面影响,在城市中产生诸如堵车、事故、噪声及废气等污染以及大量消耗能源一系列问题。这也是各个国家在发展中所必须面对的顽疾。因此,有效利用现有道路资源来缓解交通拥堵并在未来城市建设中进行合理的道路建设和交通规划,是非常值得研究的课题。本文基于细胞自动机模型,对交通流进行数值模拟,并对车辆行驶状态采用离散方程进行描述。建立了包含四个路口的二维典型城市路网的交通流模型,研究了不同道路模型中车辆间的相互影响、超车、以及信号灯控制策略等一系列影响交通流运行效率的因素。本文的主要研究内容和成果如下：1、将细胞自动机方法与跟车模型结合,研究了在单向道路上行驶的两辆不同性能车辆间的运动状态和相互关系,以及性能参数对行驶状态的影响。讨论了在设置路口和信号灯的情况下,不同信号灯控制策略(信号灯的时间周期及绿信比)对车辆运动状态的影响。研究结果表明,当信号灯恒为绿灯时,车辆相对位置关系仅与车辆的性能有关。而当信号灯周期性变化时,绿信比及信号灯时间周期等信号灯控制参数均会对车辆行驶造成不同程度的影响,特别是在考虑了车辆的加速及减速情况下的交通流模型中,增加车辆停止等待的次数会导致车辆运行效率的降低。2、在上述单车道模型的基础上,研究了双车道交通流问题,并建立了允许超车的交通流模型。分别讨论了信号灯时间周期,车辆密度等参数对车流平均速度和平均超车次数的影响。在此基础上,分析了慢车及道路障碍对交通流的影响。研究发现,道路中交通流存在保持通行效率的最优密度值,道路中车辆密度小于最优密度时,车辆数目的变化不影响交通流的平均速度。当车辆密度超过最优密度时,交通流的运动状态受密度的影响显著。当道路中车辆密度恒定时,可通过调整信号灯时间周期的方法,确保交通流的通行效率最大化。道路障碍对交通流的影响与车辆密度有关,车辆密度越大,道路障碍的影响越显著。3、研究了含有四个十字路口的二维城市典型路网的交通流问题,并通过离散方程对所建立的城市交通流模型进行描述。定义了路口容许密度,即在路口中容许占有的最大车辆数目。分别讨论了车辆密度、信号灯时间周期及路口容许密度等参数对交通流运动状态的影响。研究结果表明,对不同的交通流密度,均存在路口合理容许密度,以保证交通流获得最大运行效率。所以,适当的限制路口中的车辆密度(路口容许密度)对避免路口拥堵及死锁现象具有明显的效果,并可使交通流获得最佳的运行状态。4、研究了在二维城市典型路网的交通流模型中,信号灯控制策略与通行效率的关系。以所有车辆到达各自目的地所需消耗的平均时间最短为评价目标,研究了信号灯控制策略(同步定时控制、感应控制)及信号灯的控制参数对不同密度交通流的状态影响,并分析了不同信号灯控制策略的适用条件,以及在不同的信号灯控制策略下,道路中路口间距对交通流的影响。研究结果表明,信号灯控制方式及路口间距对交通流的影响与道路中车流密度有关,以及在低密度条件下,感应控制参数存在最优取值范围。更多还原

【Abstract】 Transportation plays an important role in the national economy and social development. Whether the transport system is modern, or traffic management is advanced, is an important symbol of modernization. With the development of economy, the number of vehicles increases rapidly with the demand of transportation. Since the 1980s, the growing traffic flow has produced several problems such as the traffic congestions, traffic accidents, energy shortages and environmental pollution. Thus, the study of traffic flow has become an interesting issue in the economic and social development. At present, governments and research institutions have paid significant attention to the effective use of the transport resources, as well as the application of scientific theories to guide the construction of transportation. Based on the cellular automata (CA) theory, the urban traffic is simulated, and the traffic dynamics is described by proposed discrete equations. A 2-D typical urban traffic model with four crossroads is established in this paper. Moreover, a set of factors affecting on the efficiency of traffic running, i.e., the interaction of vehicles, overtaking and signals control strategy, are investigated. The main contents and achievements in this paper are listed as follows:1) Combined the CA method with the car following model, this paper has proposed a vehicular movement model in one-way one-lane road, in which the time-position relation of vehicular movement states has been obtained. The interactions of two vehicles with different performances (acceleration ability and maximum allowable velocity), as well as the influence of the performance parameters on the movement states are studied. The traffic signals are also considered in this model, and the effect of signals control strategies (by changing the cycle time of traffic signal and the ratio of green time to cycle time) is discussed. The results show that when the signals are always green, the relative position of vehicles is only related to the performance of vehicles. When the signals change cyclically, the parameters such as signal’s cycle time, the ratio of green time to cycle time, et al. could affect the movement of vehicles. Especially, in the model with considering the influences of vehicular acceleration and deceleration, increasing the waiting times of vehicles will reduce the efficiency of traffic flow.2) Based on the model proposed above, two-lane traffic flow with the consideration of overtaking is investigated. Influences of signal cycle time and vehicular density on the mean velocity and mean overtaking times of traffic flow are discussed. The effects of slow vehicles and road barricades on the traffic flow are also studied. Simulation results show that the vehicular density and the signal cycle time have significant influences on the traffic flow. The mean velocity of the traffic flow could keep a comparatively large value when vehicular density is less than the optimal density. When the vehicular density exceeds the optimal density, the state of traffic flow is affected by the density significantly. For a certain value of density, the mean velocity displays a serrated fluctuation with cycle time. Therefore, there may exist a certain combination of density and cycle time which optimizes the traffic flow efficiency. The effect of barricades on traffic flow is highly related to vehicular density. The higher the vehicular density value is, the more conspicuous the effect of barricades will be.3) The 2-D typical urban traffic with consideration of four crossroads are investigated. A parameter pcross is defined which means the allowed-density of vehicles at crossing. Influences of signal cycle time, vehicular density and allowed-density of vehicles at crossing on the mean run-time, mean velocity and mean overtaking times of the traffic flow are discussed. Simulation results show that there exist certain range ofρcross which optimizes the traffic flow efficiency, and avoids traffic jam and deadlock at crossing. The model proposed here and the simulation results which took into account the effects of signal cycle time, vehicular density, density of vehicles at crossing on the traffic flow with overtaking allowed, can reflect the situation of the traffic flow in a more realistic way.4) According to the above 2-D typical urban traffic model, the effect of two signals control strategies, i.e., the fixed-time control and the actuated control are discussed. With the fixed-time control, traffic lights turn green and red synchronously, while with the actuated control, the traffic lights change according to the number of waiting vehicles on the crossroad. Based on numerical simulation, the different effects of two signals control strategies on the traffic flow and the optimal parameters of actuated signal control are discussed. Meanwhile, the effect of the intersection spacing on traffic flow with signals control is studied. Simulation results show that the effect of signals control strategies and the intersection spacing are related to the global density of traffic flow, and there exists certain optimal parameters of actuated signal control in which the efficiency of traffic flow can be optimized.更多还原