Traffic states and jamming transitions induced by a bus in two-lane traffic flow

We study the traffic states and jamming transitions induced by a bus (slow car) in a two-lane traffic of cars. We use the dynamic model which is an extended one of the optimal velocity model to take into account the lane changing. The fundamental (flow-density) diagram is presented. The fundamental diagram changes highly by introducing a bus on a two-lane roadway. It is found that there are the six distinct states for the two-lane traffic flow including a bus. The spatio-temporal patterns are presented for the distinct traffic states. The dynamical state of traffic changes with density of cars. It is shown that the dynamical transitions among the distinct traffic states occur at some values of density. The phase diagram (region map) is shown for the two-lane traffic flow including a bus.     

考虑公交港湾式停靠的多速混合城市交通流元胞自动机模型研究

在Nagel-Schreckenberg提出的元胞自动机模型基础上,建立了考虑公交车辆和港湾式公交停靠站的多速混合车辆单车道城市交通流元胞自动机模型.通过计算机模拟,给出了随机减速概率、混合车流密度、公交车辆平均停靠时间、公交车辆占有率和港湾式公交车站间距对混合车流速度和流量的影响图.对混合车流的特性进行了分析和讨论. 关键词： 元胞自动机 港湾式公交停靠站 混合交通流模型 计算机模拟     

公交车停靠诱发交通瓶颈的元胞自动机模拟

利用双车道元胞自动机模型,研究公交车停靠对道路混合交通流的影响.针对港湾式和非港湾式两种不同公交车站设置,在开放边界下模拟了公交车停靠所产生的交通瓶颈问题,给出了车辆入流概率-公交车比例相平面上的相图,区分了自由流相和拥挤相,研究了相图各区中公交车站附近的平均密度和速度分布图,比较了两种公交车站情况下的道路交通流的动力学特征.研究发现,当公交车比例较小时,与非港湾式车站相比,港湾式车站可以显著改善车站处的交通状况. 关键词： 元胞自动机 混合交通流 交通瓶颈 公交车站     

匝道系统减速车道对高速公路交通流的影响

主要研究匝道系统减速车道对高速公路交通流的影响.在开放边界条件下,以NaSch模型为基础,建立了含减速车道的出口匝道系统双车道元胞自动机交通流模型.通过计算机数值模拟,得出不同参数控制下的密度、速度、流量和车辆产生概率关系图像,并与不设减速车道的匝道系统进行比较. 关键词： 元胞自动机 匝道 减速车道 NaSch模型     

Analysis of the influence of occupation rate of public transit vehicles on mixing traffic flow in a two-lane system

Based on the existing classical cellular automaton model of traffic flow, a cellular automaton traffic model with different-maximum-speed vehicles mixed on a single lane is proposed, in which public transit and harbour-shaped bus stops are taken into consideration. Parameters such as length of cellular automaton, operation speed and random slow mechanism are re-demarcated. A harbour-shaped bus stop is set up and the vehicle changing lane regulation is changed. Through computer simulation, the influence of occupation rate of public transit vehicles on mixed traffic flow and traffic capacity is analysed. The results show that a public transport system can ease urban traffic congestion but creates new jams at the same time, and that the influence of occupation rate of public transit vehicles on traffic capacity is considerable. To develop urban traffic, attention should be paid to the occupation rate of public transit vehicles and traffic development in a haphazard way should be strictly avoided.     

两车道交通流耦合格子模型与数值仿真

考虑两车道耦合效应的影响和换道效应,提出了改进的两车道交通流耦合格子模型.同时,改进了换道时的流量转移率,这样更符合实际交通情况.通过线性稳定性分析,得到了改进模型的稳定性条件.数值模拟结果也表明,模型通过考虑耦合作用信息,更好地再现了换道情况,同时也表明两车道间的耦合效应对两车道交通流存在不可忽视的影响.     

Influence of bus stop with left-turn lines between two adjacent signalized intersections

Based on the symmetric two-lane Nagel–Schreckenberg(STNS) model, a three-lane cellular automaton model between two intersections containing a bus stop with left-turning buses is established in which model the occurrences of vehicle accidents are taken into account. The characteristics of traffic flows with different ratios of left-turn lines are discussed via the simulation experiments. The results indicate that the left-turn lines have more negative effects on capacity,accident rate as well as delay if the stop is located close to the intersections, where the negative effect in a near-side stop is more severe than that in a far-side one. The range of appropriate position for a bus stop without the bottleneck effect becomes more and more narrow with the increase of the ratio of left-turn bus lines. When the inflow is small, a short signal cycle and a reasonable offset are beneficial. When the inflow reaches or exceeds the capacity, a longer signal cycle is helpful. But if the stop position is inappropriate, the increase of cycle fails in reducing the negative effect of left-turning buses and the effectiveness of offset is weakened.     

A study on the effects of the transit parking time on traffic flow based on cellular automata theory

This paper mainly deals with the effects of transit stops on vehicle speeds and conversion lane numbers in a mixed traffic lane.Based on thorough research of traffic flow and cellular automata theory,it calibrates the cellular length and the running speed.Also,a cellular automata model for mixed traffic flow on a two-lane system under a periodic boundary condition is presented herewith,which also takes into consideration the harbour-shaped transit stop as well.By means of computer simulation,the article also studies the effects of bus parking time on the traffic volume,the transit speed and the fast lane speed at the same time.The results demonstrate that,with the increase of the bus parking time,the traffic volume of the transit stop and the transit speed decrease while the fast lane speed increases.This result could help calculate the transit delay correctly and make arrangements for transit routes reasonably and scientifically.     

Continuum modeling for two-lane traffic flow with consideration of the traffic interruption probability

Considering the effects that the probability of traffic interruption and the friction between two lanes have on the car-following behaviour,this paper establishes a new two-lane microscopic car-following model.Based on this microscopic model,a new macroscopic model was deduced by the relevance relation of microscopic and macroscopic scale parameters for the two-lane traffic flow.Terms related to lane change are added into the continuity equations and velocity dynamic equations to investigate the lane change rate.Numerical results verify that the proposed model can be efficiently used to reflect the effect of the probability of traffic interruption on the shock,rarefaction wave and lane change behaviour on two-lane freeways.The model has also been applied in reproducing some complex traffic phenomena caused by traffic accident interruption.     

Combined bottleneck effect of on-ramp and bus stop in a cellular automaton model

The combined bottleneck effect is investigated by modeling traffic systems with an on-ramp and a nearby bus stop in a two-lane cellular automaton model. Two cases, i.e. the bus stop locates in the downstream section of the on-ramp and the bus stop locates in the upstream section of the on-ramp, are considered separately. The upstream flux and downstream flux of the main road, as well as the on-ramp flux are analysed in detail, with respect to the entering probabilities and the distance between the on-ramp and the bus stop. It is found that the combination of the two bottlenecks causes the capacity to drop off, because the vehicles entering the main road from the on-ramp would interweave with the stopping (pulling-out) buses in the downstream (upstream) case. The traffic conflict in the former case is much heavier than that in the latter, causing the downstream main road to be utilized inefficiently. This suggests that the bus stop should be set in the upstream section of the on-ramp to enhance the capacity. The fluxes both on the main road and on the on-ramp vary with the distance between the two bottlenecks in both cases. However, the effects of distance disappear gradually at large distances. These findings might give some guidance to traffic optimization and management.     

Mitigation of congestion at a traffic bottleneck with diversion and lane restrictions

Mitigation of congestion on a two-lane highway with an off-ramp and an on-ramp is simulated with three-phase traffic theory. Advanced travel information-the average velocity of vehicles near the bottleneck at an on-ramp-is used to divert vehicles at an upstream off-ramp. If enough vehicles divert, previously expanding synchronous flow congestion can be stalled and isolated to the region between the ramps. The introduction of lane restrictions (forbidding lane changing on the portion of highway between the ramps) in addition to diversion substantially reduces and essentially eliminates the congestion, restoring flow to nearly free-flow conditions.     

A Two-Lane Cellular Automata Model with Influence of Next-Nearest Neighbor Vehicle

In this paper, we propose a new two-lane cellular automata model in which the influence of the next-nearest neighbor vehicle is considered. The attributes of the traffic system composed of fast-lane and slow-lane are investigated by the new traffic model. The simulation results show that the proposed two-lane traffic model can reproduce some traffic phenomena observed in real traffic, and that maximum flux and critical density are close to the field measurements.Moreover, the initial density distribution of the fast-lane and slow-lane has much influence on the traffic flow states.With the ratio between the densities of slow lane and fast lane increasing the lane changing frequency increases, but maximum flux decreases. Finally, the influence of the sensitivity coefficients is discussed.     

The Stability of Multi-modal Traffic Network

There is an explicit and implicit assumption in multimodal traffic equilibrium models, that is, if the equilibrium exists, then it will also occur. The assumption is very idealized; in fact, it may be shown that the quite contrary could happen, because in multimodal traffic network, especially in mixed traffic conditions the interaction among traffic modes is asymmetric and the asymmetric interaction may result in the instability of traffic system. In this paper, to study the stability of multimodal traffic system, we respectively present the travel cost function in mixed traffic conditions and in traffic network with dedicated bus lanes. Based on a day-to-day dynamical model, we study the evolution of daily route choice of travelers in multimodal traffic network using 10000 random initial values for different cases. From the results of simulation, it can be concluded that the asymmetric interaction between the cars and buses in mixed traffic conditions can lead the traffic system to instability when traffic demand is larger. We also study the effect of travelers' perception error on the stability of multimodal traffic network. Although the larger perception error can alleviate the effect of interaction between cars and buses and improve the stability of traffic system in mixed traffic conditions, the traffic system also become instable when the traffic demand is larger than a number. For all cases simulated in this study, with the same parameters, traffic system with dedicated bus lane has better stability for traffic demand than that in mixed traffic conditions. We also find that the network with dedicated bus lane has higher portion of travelers by bus than it of mixed traffic network. So it can be concluded that building dedicated bus lane can improve the stability of traffic system and attract more travelers to choose bus reducing the traffic congestion.     

The Stability of Multi-modal Traffic Network

There is an explicit and implicit assumption in multimodal traffic equilibrium models, that is, if the equilibrium exists, then it will also occur. The assumption is very idealized; in fact, it may be shown that the quite contrary could happen, because in multimodal traffic network, especially in mixed traffic conditions the interaction among traffic modes is asymmetric and the asymmetric interaction may result in the instability of traffic system. In this paper, to study the stability of multimodal traffic system, we respectively present the travel cost function in mixed traffic conditions and in traffic network with dedicated bus lanes. Based on a day-to-day dynamical model, we study the evolution of daily route choice of travelers in multimodal traffic network using 10000 random initial values for different cases. From the results of simulation, it can be concluded that the asymmetric interaction between the cars and buses in mixed traffic conditions can lead the traffic system to instability when traffic demand is larger. We also study the effect of travelers' perception error on the stability of multimodal traffic network. Although the larger perception error can alleviate the effect of interaction between cars and buses and improve the stability of traffic system in mixed traffic conditions, the traffic system also become instable when the traffic demand is larger than a number. For all cases simulated in this study, with the same parameters, traffic system with dedicated bus lane has better stability for traffic demand than that in mixed traffic conditions. We also find that the network with dedicated bus lane has higher portion of travelers by bus than it of mixed traffic network. So it can be concluded that building dedicated bus lane can improve the stability of traffic system and attract more travelers to choose bus reducing the traffic congestion.     

考虑驾驶心理的城市双车道交通流元胞自动机模型

采用双车道元胞自动机模型,分析了考虑驾驶心理的城市道路交通流特性.针对驾驶员在城市道路行驶时在换道与减速制动方面的不同心理,分别引入了反映驾驶心理的选择换道概率P_s与安全参数λ.通过计算机模拟,给出了不同选择换道概率与安全参数条件下的车辆速度、密度与流量间的关系,并分析了不同驾驶心理对于交通系统的影响.研究发现:选择换道概率对交通流的速度影响并不明显,但选择换道概率的增大会导致速度的方差增大而降低行车安全;而安全参数的增大可以获得更快的平均车速和更大的交通 关键词： 元胞自动机 驾驶心理 选择换道概率 计算机模拟     

Extended speed gradient model for traffic flow on two-lane freeways

In this paper, the speed gradient (SG) model is extended to describe the traffic flow on two-lane freeways. Terms related to lane change are added into the continuity equations and velocity dynamic equations. The empirically observed two-lane phenomena, such as lane usage inversion and lane change rate versus density, are reproduced by extended SG model. The local cluster effect is also investigated by numerical simulations.     

Safety-collision transition induced by lane changing in traffic flow

We study the traffic behavior when a vehicle changes from the first lane to the second lane on a two-lane highway. We apply the optimal velocity model to the vehicular motion. If the incoming vehicle does not decelerate successfully, it crashes into the vehicle ahead. On the other hand, if the headway between the incoming vehicle and the vehicle behind on the second lane is not long sufficiently, the rear vehicle may come into collision with the incoming vehicle. The safety-collision transition occurs by changing the lane. The dynamical transition depends highly on the vehicular speed, the sensitivity, and the headway. We derive the phase diagram (or region map) for the safety-collision transition.     

The effects of accelerating lane in the on-ramp system

Usually there is an accelerating lane as an on-ramp merges with the main road. How the length of this section and the traffic regulations influence the traffic behaviors has seldom been investigated. In this paper, we study this issue using the cellular automata traffic flow model. We find that (i) the permission of lane changing from main road to the accelerating lane will deteriorate the capacity of the road, hence it should be forbidden; (ii) when lane changing from main road to accelerating lane is forbidden, the introduction of an accelerating lane can improve the capacity of the on-ramp system.     

The capacity of two neighbour intersections considering the influence of the bus stop

In this paper, we use a two-lane CA model to investigate the effect of a bus stop between two neighbouring intersections on the capacity of the bus. Both the case of a bus stop with a special stopping lane and that of one without are considered. The capacity versus the distance L_B(L_D) between the stop and the upstream (downstream) intersection is studied, with respect to the entering probability P_e and the traffic light cycle T. It is found that a bus stop near an intersection can act as a bottleneck and cause a drop in the capacity when the L_B (or L_D) is below a critical point L_Bc1(or L_Dc1). However, the situation when the stop is located near the downstream intersection is worse than that of the upstream one. Furthermore, the simulation results show that the negative effect varies with the increase of the cycle time T and the capacity can be maximized by adjusting T. Comparisons between the two cases suggest that the stopping lane can improve the capacity to some extent. These results mean that the capacity can be exploited by changing the position of the bus stop or the cycle time, and adding a stopping lane if necessary. These findings may be useful in offering scientific guidance for the management and design of traffic networks.