Effects of connected automated vehicle on stability and energy consumption of heterogeneous traffic flow system

With the development of intelligent and interconnected traffic system,a convergence of traffic stream is anticipated in the foreseeable future,where both connected automated vehicle(CAV)and human driven vehicle(HDV)will coexist.In order to examine the effect of CAV on the overall stability and energy consumption of such a heterogeneous traffic system,we first take into account the interrelated perception of distance and speed by CAV to establish a macroscopic dynamic model through utilizing the full velocity difference(FVD)model.Subsequently,adopting the linear stability theory,we propose the linear stability condition for the model through using the small perturbation method,and the validity of the heterogeneous model is verified by comparing with the FVD model.Through nonlinear theoretical analysis,we further derive the KdV-Burgers equation,which captures the propagation characteristics of traffic density waves.Finally,by numerical simulation experiments through utilizing a macroscopic model of heterogeneous traffic flow,the effect of CAV permeability on the stability of density wave in heterogeneous traffic flow and the energy consumption of the traffic system is investigated.Subsequent analysis reveals emergent traffic phenomena.The experimental findings demonstrate that as CAV permeability increases,the ability to dampen the propagation of fluctuations in heterogeneous traffic flow gradually intensifies when giving system perturbation,leading to enhanced stability of the traffic system.Furthermore,higher initial traffic density renders the traffic system more susceptible to congestion,resulting in local clustering effect and stop-and-go traffic phenomenon.Remarkably,the total energy consumption of the heterogeneous traffic system exhibits a gradual decline with CAV permeability increasing.Further evidence has demonstrated the positive influence of CAV on heterogeneous traffic flow.This research contributes to providing theoretical guidance for future CAV applications,aiming to enhance urban road traffic efficiency and alleviate congestion.

Research on the Optimization Control Method of Inbound Traffic Flow on On-ramp

This study aims to optimize the inbound traffic flow on on-ramps by considering low time costs,good speed stability,and high driving safety for mixed traffic flow.The optimal inlet gap is identified in advance,and trajectory guidance for vehicles entering the gap is determined under safety constraints.Based on the initial state and sequence of vehicles entering the merging area,individual vehicle trajectories are optimized sequentially.An optimization model and method for ramp entry trajectories in mixed traffic flow are developed,incorporating on-ramp vehicle entry sequencing and ordinary vehicle trajectory prediction.Key performance indicators,including driving safety,total travel time,parking wait probability,and trajectory smoothness,are compared and analyzed to evaluate the proposed approach.

Effects of the number of on-ramps on the ring traffic flow

Since ramps are an important composition of traffic systems and there often exist multi ramps in a tragic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang et al. [2009 Communications in Theoretical Physics 51（1） 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex tragic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.

Stability analysis of traffic flow with extended CACC control models

To further investigate car-following behaviors in the cooperative adaptive cruise control（CACC） strategy,a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models.In this control system,some vital comprehensive information,such as multiple preceding cars’ speed differences and headway,variable safety distance（VSD） and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods.Local and string stability criterion for the velocity control（VC） model and gap control（GC） model are derived via linear stability theory.Numerical simulations are conducted to study the performance of the simulated traffic flow.The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion.

A Lane Change Model Considering the Stability of Cooperative Adaptive Cruise Control Platoon Fleet

In this article,lane change models for mixed traffic flow under cooperative adaptive cruise control(CACC)platoon formation are established.The analysis begins by examining the impact of lane changes on traffic flow stability.The influences of various factors such as lane change locations,timing,and the current traffic state on stability are discussed.In this analysis,it is assumed that the lane change location and the entry position in the adjacent lane have already been selected,without considering the specific intention behind the lane change.The speeds of the involved vehicles are adjusted based on an existing lane change model,and various conditions are analyzed for traffic flow disturbances,including duration,shock amplitude,and driving delays.Numerical calculations are provided to illustrate these effects.Additionally,traffic flow stability is factored into the lane change decision-making process.By incorporating disturbances to the fleet into the lane change income model,both a lane change intention model and a lane change execution model are constructed.These models are then compared with a model that does not account for stability,leading to the corresponding conclusions.

Lane changing analysis for two-lane traffic flow

In this paper, the two-lane traffic are studied by using the lane-changing rules in the car-following models. The simulation show that the frequent lane changing occurs when the lateral distance in car following activities is considered and it gives rise to oscillating waves. In contrast, if the lateral distance is not considered （or considered occasionally）, the lane changing appears infrequently and soliton waves occurs. This implies that the stabilization mechanism no longer functions when the lane changing is permitted. Since the oscillating and soliton waves correspond to the unstable and metastable flow regimes, respectively, our study verifies that a phase transition may occur as a result of the lane changing.

Effect of multi-velocity-difference in traffic flow

Based on the optimal velocity models, an extended model is proposed, in which multi-veloclty-dllterence aheacl is taken into consideration. The damping effect of the multi-velocity-difference ahead has been investigated by means of analytical and numerical methods. Results indicate that the multi-velocity-difference leads to the enhancement of stability of traffic flow, suppression of the emergence of traffic jamming, and reduction of the energy consumption.

Detailed string stability analysis for bi-directional optimal velocity model

The class of bi-directional optimal velocity models can describe the bi-directional looking effect that usually exists in the reality and is even enhanced with the development of the connected vehicle technologies. Its combined string stability condition can be obtained through the method of the ring-road based string stability analysis. However, the partial string stability about traffic fluctuation propagated backward or forward was neglected, which will be analyzed in detail in this work by the method of transfer function and its H∞ norm from the viewpoint of control theory. Then, through comparing the conditions of combined and partial string stabilities, their relationships can make traffic flow be divided into three distinguishable regions, displaying various combined and partial string stability performance. Finally, the numerical experiments verify the theoretical results and find that the final displaying string stability or instability performance results from the accumulated and offset effects of traffic fluctuations propagated from different directions.

Dynamic characteristics and simulation of traffic flow with slope

This paper proposes a new traffic model to describe traffic flow with slope under consideration of the gravity effect.Based on the model,stability analysis is conducted and a numerical simulation is performed to explore the characteristics of the traffic flow with slope.The result shows that the perturbation of the system is an inherent one,which is induced by the slope.In addition,the hysteresis loop is represented through plotting the figure of velocity against headway and highly depends on the slope angle. The kinematic wave at high density is also obtained through reproducing the phenomenon of stop-and-go traffic,which is significant to explore the phase transition of traffic flow and the evolution of traffic congestion.

A New Macro Model for Traffic Flow on a Highway with Ramps and Numerical Tests

In this paper, we present a new macro model for traffic flow on a highway with ramps based on the existing models. We use the new model to study the effects of on-off-ramp on the main road traffic during the morning rush period and the evening rush period. Numerical tests show that, during the two rush periods, these effects are often different and related to the status of the main road traffic. If the main road traffic flow is uniform, then ramps always produce stop-and-go traffic when the main road density is between two critical values, and ramps have little effect on the main road traffic when the main road density is less than the smaller critical value or greater than the larger critical value. If a small perturbation appears on the main road, ramp may lead to stop-and-go traffic, or relieve or even eliminate the stop-and-go traffic, under different circumstances. These results are consistent with real traffic, which shows that the new model is reasonable.

A New Macro Model for Traffic Flow on a Highway with Bus Stop

Based on the difference between the online bus stop and the offline bus stop, two macro models are developed to describe the two types of bus stops. The numerical results show that the two models can qualitatively reproduce some complex phenomena resulted by the two types of bus stops and that the otttine bus stop is more effective than the online bus stop when the initial density is relatively low.

Efficiency promotion for an on-ramp system based on intelligent transportation system information

Effect of cars with intelligent transportation systems （ITSs） on traffic flow near an on-ramp is investigated by car-following simulations. By numerical simulations, the dependences of flux on the inflow rate are investigated for various proportions of cars with ITSs. The phase diagrams as well as the spatiotemporal diagrams are presented to show different traffic flow states on the main road and the on-ramp. The results show that the saturated flux on the main road increases and the free flow region is enlarged with the increase of the proportion of cars with ITS. Interestingly, the congested regions of the main road disappear completely when the proportion is larger than a critical value. Further investigation shows that the capacity of on-ramp system can be promoted by 13% by using the ITS information, and the saturated flux on the on-ramp can be kept at an appropriate value by adjusting the proportion of cars with ITS.

Stabilization of Traffic Flow Based on the Multiple Information of Preceding Cars

To enhance the stability of traffic flow,a new car-following model is proposed by taking into account the support of intelligent transportation system(ITS)information,which includes both the headway and the velocity difference of multiple preceding cars.The new model is based on the Optimal Velocity(OV)model and its extended models.The stability condition of the model is obtained by using the linear stability theory.Through nonlinear analysis,the modified Korteweg-de Vries equation is constructed and solved,and the traffic flow is classified into three types,i.e.stable,metastable,and unstable.The jam phase can thus be described by the kink-antikink soliton solution for the mKdV equation.The numerical simulation results show that compared with previous models considering only one of the ITS information,the proposed model can suppress traffic jams more efficiently when both headway and velocity difference of arbitrary preceding cars are taken into account.The results of numerical simulation coincide with the theoretical ones.

Microscopic car-following model for the traffic flow:the state of the art

Car following theory is an important research direction in the field of intelligent transportation systems （ITS）, it describes the one-by-one following process of vehicles on the same lane in traffic flow, and one of its important issues is congestion control To explore the strategy for controlling traffic congestion, this paper introduces and analyzes some classic car following models, and gives a systematic review of their developments. Moreover, in order to introduce the approach to analyze the stability, taking the full velocity difference （FVD） model for example, the local and asymptotic stability analysis is discussed, while the corresponding nonlinear analysis is also conducted. Then, some perspectives of the car following model are given in the final.

A Macro Model for Traffic Flow with Consideration of Static Bottleneck

In this paper, we develop a macro model for traffic flow with consideration of static bottleneck to explore the impacts of static bottleneck on traffic flow. The analytical and numerical results show that the proposed model can qualitatively describe the equilibrium flux, uniform flow and small perturbation under the action of a static bottleneck.

Analyses of Lattice Traffic Flow Model on a Gradient Highway

The optimal current difference lattice hydrodynamic model is extended to investigate the traffic flow dynamics on a unidirectional single lane gradient highway. The effect of slope on uphill/downhill highway is examined through linear stability analysis and shown that the slope significantly affects the stability region on the phase diagram.Using nonlinear stability analysis, the Burgers, Korteweg-deVries(KdV) and modified Korteweg-deVries(mKdV) equations are derived in stable, metastable and unstable region, respectively. The effect of reaction coefficient is examined and concluded that it plays an important role in suppressing the traffic jams on a gradient highway. The theoretical findings have been verified through numerical simulation which confirm that the slope on a gradient highway significantly influence the traffic dynamics and traffic jam can be suppressed efficiently by considering the optimal current difference effect in the new lattice model.

Nonlinear analysis of traffic jams in an anisotropic continuum model

This paper presents our study of the nonlinear stability of a new anisotropic continuum traffic flow model in which the dimensionless parameter or anisotropic factor controls the non-isotropic character and diffusive influence. In order to establish traff^c flow stability criterion or to know the critical parameters that lead, on one hand, to a stable response to perturbations or disturbances or, on the other hand, to an unstable response and therefore to a possible congestion, a nonlinear stability criterion is derived by using a wavefront expansion technique. The stability criterion is illustrated by numerical results using the finite difference method for two different values of anisotropic parameter. It is also been observed that the newly derived stability results are consistent with previously reported results obtained using approximate linearisation methods. Moreover, the stability criterion derived in this paper can provide more refined information from the perspective of the capability to reproduce nonlinear traffic flow behaviors observed in real traffic than previously established methodologies.

Safety benefit of cooperative control for heterogeneous traffic on-ramp merging

The safety of heterogeneous traffic is a vital topic in the oncoming era of autonomous vehicles(AVs).The cooperative vehicle infrastructure system(CVIS)is considered to improve heterogeneous traffic safety by connecting and controlling AVs cooperatively,and the connected AVs are so-called connected and automated vehicles(CAVs).However,the safety impact of cooperative control strategy on the heterogeneous traffic with CAVs and human-driving vehicles(HVs)has not been well investigated.In this paper,based on the traffic simulator SUMO,we designed a typical highway scenario of on-ramp merging and adopted a cooperative control method for CAVs.We then compared the safety performance for two different heterogeneous traffic systems,i.e.AV and HV,CAV and HV,respectively,to illustrate the safety benefits of the cooperative control strategy.We found that the safety performance of the CAV and HV traffic system does not always outperform that of AV and HV.With random departSpeed and higher arrival rate,the proposed cooperative control method would decrease the conflicts significantly whereas the penetration rate is over 80%.We further investigated the conflicts in terms of the leading and following vehicle types,and found that the risk of a AV/CAV followed by a HV is twice that of a HV followed by another HV.We also considered the safety effect of communication failure,and found that there is no significant impact until the packet loss probability is greater than 30%,while communication delay’s impact on safety can be ignored according to our experiments.

考虑前后多车的混合交通流稳定性与安全性分析

为揭示前后多车信息对复杂混合交通流稳定性与安全性的影响,本文构建考虑前后多车信息的网联自动驾驶车辆(CAV)与网联人工驾驶车辆(CHV)跟驰模型,研究由人工驾驶车辆(HDV)、自动驾驶车辆(AV)、CAV和CHV构成的复杂混合交通流的稳定性与安全性。首先,建立考虑前后多车信息的复杂混合交通流模型,分析所有跟驰模式及4种类型车辆的比例关系;其次,理论解析不同网联车辆渗透率下复杂混合交通流的稳定性判别条件;最后,设计数值实验,分析网联车辆渗透率与前后多车信息对复杂混合交通流稳定性与安全性的影响。仿真结果表明:CAV与CHV渗透率越高,越有利于复杂混合交通流的稳定性,且CHV对复杂混合交通流稳定性改善效果比CAV更显著;相比于仅考虑紧邻前后车信息的情形,考虑前后多车信息对复杂混合交通流的稳定性与安全性具有较大的改善作用;考虑前后两辆车信息时,复杂混合交通流的稳定性与安全性改善效果最佳。

考虑加减速行为不对称的终端区空中交通流跟驰模型

为精细化描述空中交通流跟驰行为,考虑空中交通加减速跟驰行为的不对称性,本文提出一种基于改进智能驾驶员模型(Intelligent Driver Model,IDM)的空中交通流跟驰模型。采用成都终端区实际航迹数据,筛选出跟驰航迹数据;在此基础上,应用遗传算法对经典跟驰模型进行参数标定,选取出IDM模型的拟合精度最好;进而,考虑加速度、前后机间隔、平均速度差和机型等因素,分别构建加速和减速场景下的改进IDM跟驰模型;最后,采用奈奎斯特图分析改进模型的局部稳定性和渐近稳定性,并对加减速场景下的改进跟驰模型进行仿真实验。结果表明,改进IDM模型的稳定范围增大,且在加速和减速场景下,改进IDM模型所需稳定时间分别仅为原始IDM模型的13.9%和22.2%,头机为不同机型时,模型均表现较强稳定性,且头机为重型机时,所需稳定时间最长,这与实际运行中重型机产生的尾流对后机影响最为严重相一致。