多路段元胞自动机交通流模型

在经典单路段元胞自动机交通流模型的基础上,将多个路段视为一个道路系统,提出并研究了多路段条件下的交通流问题.针对多路段道路的特点,通过引入车辆流入规则、路口随机慢化规则和路口车辆流入规则,控制车辆从上一路段流入下一路段.首先提出了"汽车池"的概念,来控制每一路口车辆的流入;然后通过路口随机慢化,来模拟路口对交通的影响;最后,当车辆离开时,依直行率进入下一路段,实现车流的继续流动.同时,通过数值模拟,仿真了不同条件下的交通情况,对重要参数进行了研究.结果表明,出现了混合流这一新的现象,拥堵地段与非拥堵地段间存在明显的界限.拥堵往往最先从路口开始,然后蔓延到整个路段.多路段道路还存在临界突变的特性.随着车辆流入概率的增大,路口对平均速度和车流密度的影响愈加明显.当流入概率超过一定阈值时,车辆缓慢地增加也会引起整体道路通行能力的迅速下降.

Multi-section cellular automata model of traffic flow

It is more common for drivers to pass through multiple sections to reach destinations instead of single road section. Howerver, most of researches concentrate on improving the effect in an independent section. Based on traditional cellular automata traffic model, a multi-section model is proposed by regarding serverl road sections as a traffic system. In this model, different sections of the road might have different lengths, numbers of lanes or maximal speeds. And vehicles travel from one section to another. The main difficulty lies in dealing with the relationships among the traffic flows of different sections. Besides basic rules in NaSch model, the vehicle inflow rule, crossroad randomization brake rule and crossroad inflow rule is added in this paper to enable vehicles to flow between sections. At the beginning of section, to avoid conflicting at crossroads under open boundary condition, the concept of car pool is introduced when new vehicles enter into sections. Before arriving at the end of section, crossroad randomization brake is used to simulate the influences of crossroads. Speed decreases in probability until lower than a maximal crossroad speed. When leaving the section, vehicles go to the next section with a straight ratio. Also, new vehicles may enter according to traffic condition. Therefore, cellular automata of different sections can be connected in series.Finally, numerical simulation is demonstrated to study the influences of important parameters, including traffic inflow probability, maximal crossroad speed and crossroad randomization brake probability. Compared with traditional models, this model focuses on connecting sections. And improvements of basic models can be implanted easily, thereby increasing the accuracy of the whole model in the future. The experimental result are as follows. 1) According to space-time graphs of different inflow probabilities, there is a new kind of traffic flow called mixed flow. Traffic congestion often starts from crossroads, and spreads to the whole section. And traffic jams in previous section might relieve traffic pressure in latter section. 2) With the increase of traffic inflow probability, crossroads tends to have a greater influence on average speed as well as average traffic density. What is more, the moderate increase of vehicle numbers could cause the road capacity to drop rapidly if it exceeds the threshold value.