Constant Time Headway Research Articles

Platooning Control for Heterogeneous Sailboats Based on Constant Time Headway

This paper addresses the problem of platooning control for a fleet of heterogeneous sailboats. The platooning maintains a constant time headway (CTH) between sailboats following a circular path, a complex problem for sailboats due to the influence of wind direction. First, the desired acceleration based on the CTH and the sailboat velocity needed to converge to the platooning is defined. Second, a control of sailboat orientation to manage the sailboat acceleration is proposed. The proposed platooning strategy adapts to the specific characteristics of sailboats, which are different from other motorized marine vehicles. Two tack strategies can be used for the method: the first is to regulate the sailboat velocity; the second is to go front of the wind while staying in a short corridor. The desired acceleration for fulfilling the platooning has been derived and validated. The simulation results demonstrate the effectiveness of the proposed approach in comparison with an optimal receding horizon control algorithm.

Benefits of V2V Communication for Autonomous and Connected Vehicles

In this paper, we investigate the benefits of vehicle-to-vehicle (V2V) communication for autonomous vehicles and provide results on how V2V information helps reduce employable time headway in the presence of parasitic lags. For a string of vehicles adopting a constant time headway policy and availing the on-board information of predecessor’s vehicle position and velocity, the minimum employable time headway ( $h_{\min }$ ) must be lower bounded by $2\tau _{0}$ for string stability, where $\tau _{0}$ is the maximum parasitic actuation lag. In this paper, we quantify the benefits of using V2V communication in terms of a reduction in the employable time headway: 1) If the position and velocity information of $r$ immediately preceding vehicles is used, then $h_{\min }$ can be reduced to ${4\tau _{0}}/{(1+r)}$ ; 2) furthermore, if the acceleration of ‘ $r$ ’ immediately preceding vehicles is used, then $h_{\min }$ can be reduced to ${2\tau _{0}}/{(1+r)}$ ; and 3) if the position, velocity, and acceleration of the immediate and the $r$ -th predecessors are used, then $h_{\min } \ge {2\tau _{0}}/{(1+r)}$ . Note that cases (2) and (3) provide the same lower bound on the minimum employable time headway; however, case (3) requires much less communicated information.

Reducing time headway for platooning of connected vehicles via V2V communication

In a platoon of connected vehicles, time headway plays an important role in both traffic capacity and road safety. It is desirable to maintain a lower time headway while satisfying string stability in a platoon, since this leads to a higher traffic capacity and guarantees the disturbance attenuation ability. In this paper, we study a multiple-predecessor following strategy to reduce time headway via vehicle-to-vehicle (V2V) communication. We first introduce a new definition of desired inter-vehicle distances based on the constant time headway (CTH) policy, which is suitable for general communication topologies. By exploiting lower-triangular structures in a time headway matrix and an information topology matrix, we derive a set of necessary and sufficient conditions on feedback gains for internal asymptotic stability. Further, by analyzing the stable region of feedback gains, a necessary and sufficient condition on time headway is also obtained for the string stability specification. It is proved that a platoon can be asymptotically stable and string stable when the time headway is lower bounded. Moreover, this bound can be reduced by increasing the number of predecessors. These results explicitly highlight the benefits of V2V communication on reducing time headway for platooning of connected vehicles.

Hierarchical Fuzzy Logic-Based Variable Structure Control for Vehicles Platooning

This paper proposes a variable structure control approach for vehicles platooning based on a hierarchical fuzzy logic. The leader-follower vehicle dynamics with model uncertainties is discussed from the viewpoint of a consensus problem. A practical two-layer fuzzy control for the platooning is designed by employing two common spacing policies to ensure system robustness in different scenarios. The two policies, i.e., constant distance and constant time headway, utilize the predecessor-successor information flow from the immediate predecessor and follower other than controlled vehicles. The first layer of the fuzzy system combines spacing control with velocity-acceleration control to achieve a rapid tracking for the desired control commands, and the second layer combines the sliding mode control to adaptively compensate for reducing the state errors caused by parameter uncertainties and disturbances. Shift between different controller parameters is based on performance boundaries to guarantee the stability of individual vehicle and platooning for arbitrary initial spacing and velocity errors. These performance boundaries can be determined by using a Lyapunov method with exponential stability. Simulation of a ten-vehicle large platooning with two spacing policies shows that the control performance of the newly proposed method is effective and promising.

String Stable Vehicle Platooning Using Adaptive Cruise Controlled Vehicles

Abstract Vehicle grouping in platoons and their automated control lead to reduced distances between vehicles with benefits in terms of increasing the capacity of roads and decreasing the fuel consumption and pollutant emissions. Reducing the distance must be done in compliance with safety rules, a condition being the string stability of the interconnected vehicles that make up the platoon. This paper presents a Linear Quadratic Integral Regulator for homogeneous platoon of ACC vehicles, which can guarantee the desired tracking performance and string stability requirement. By introducing a double integrator in the control law, tracking performance is obtained and a heuristic method is proposed for string stability by the selection of the constant time headway (CTH). The CTH selection for string stability is based on the Nyquist diagram and the pole-zero map of the transfer function of the spacing errors between two adjacent vehicles. The method was used for the comparative analysis of the string stability of autonomous vehicles using two ACC structures based on position and, respectively, on distance.

Neuroadaptive quantized PID sliding‐mode control for heterogeneous vehicular platoon with unknown actuator deadzone

SummaryThis paper focuses on the problem of neuroadaptive quantized control for heterogeneous vehicular platoon when the follower vehicles suffer from external disturbances, mismatch input quantization, and unknown actuator deadzone. The PID‐based sliding‐mode (PIDSM) control technique is used due to its superior capability to reduce spacing errors and to eliminate the steady‐state spacing errors. Then, a neuroadaptive quantized PIDSM control scheme with minimal learning parameters is designed not only to guarantee the string stability of the whole vehicular platoon and ultimate uniform boundedness of all adaptive law signals but also to attenuate the negative effects caused by external disturbance, mismatch input quantization, and unknown actuator deadzone. Furthermore, optimizing the interspacing between consecutive vehicles is very important to reduce traffic congestion on highways, and a new modified constant time headway policy is proposed to not only increase traffic density but also address the negative effect of nonzero initial spacing, velocity, and acceleration errors. Compared with most existing methods, the proposed method does not linearize the system model and neither requires precise knowledge of the system model. Finally, the effectiveness and advantage of the proposed method are demonstrated by comparative simulation studies.

Vehicle-to-vehicle based multi-objective coordinated adaptive cruise control considering platoon stability

Currently, there is a widespread concern over cooperative driving based on vehicle-to-vehicle communication due to its considerable potential to improve the increased traffic safety, efficiency, costs, and intellectualization. In this article, a multi-objective coordinated adaptive cruise control algorithm for a string of adaptive cruise control–equipped vehicles is thus proposed, which can comprehensively address issues regarding homogeneous/heterogeneous features, road capacity, in addition to driver desired response. The practical platoon stability of adaptive cruise control–equipped vehicles employing constant time headway spacing policy is investigated by taking into account the parasitic time delays of wireless communication modules and time lags of automotive actuators. The simulations show that the control algorithm utilizing model predictive control framework reaps significant benefits in terms of driver desired response, platoon stability as well as road capacity, while at the same time providing a reasonable proposal on the design of adaptive cruise control controller with better adaptability from the perspective of practical platoon stability.

CNN-Based Distributed Adaptive Control for Vehicle-Following Platoon With Input Saturation

A neural network-based distributed adaptive approach combined with sliding mode technique is proposed for vehicle-following platoons in the presence of input saturation, unknown unmodeled nonlinear dynamics, and external disturbances. A simple and straightforward strategy by adjusting only a single parameter is proposed to compensate for the effect of input saturation. Two spacing polices (i.e., traditional constant time headway policy and modified constant time headway policy) are used to guarantee string stability and maintain the desired spacing. Chebyshev neural networks (CNN) are used to approximate the unknown nonlinear functions in the followers online, and the implementation of the basic functions of CNN depends only on the leader’s velocity and acceleration. Furthermore, unlike existing approaches, the nonlinearities of consecutive vehicles need not satisfy the matching condition. Finally, simulations are carried out to illustrate the effectiveness and the advantage of the proposed methods, first using a numerical example, followed by a practical example of a high speed train platoon.

Adaptive Centralized/Decentralized Control and Identification of 1-D Heterogeneous Vehicular Platoons Based on Constant Time Headway Policy

This paper deals with the adaptive control and identification of 1-D platoon of non-identical vehicles. Three common different topologies, such as predecessor following, bi-directional leader following, and two predecessors following are considered as the communication structures of platoon. For each topology, a new neighbor-based adaptive control law is introduced to estimate the parameter uncertainties, such as rolling resistance and air drag force coefficients. By presenting a new theorem, we prove that the estimates of unknown parameters converge to the actual values. Constant time headway policy is used to adjust the inter-vehicle spacing. For each topology, it is shown that the closed-loop dynamics of platoon is asymptotically stable. Afterward, the necessary conditions on control parameters assuring the string stability for each topology are derived by presenting further theorems. Moreover, the proposed methods are generalized for the heterogeneous platoons with time-varying network topology. Simulation results with different scenarios are provided to show the effectiveness of the presented approaches.

A Platooning Strategy for Automated Vehicles in the Presence of Speed Limit Fluctuations

Platooning is expected to enhance the efficiency of operating automated vehicles. The positive impacts of platooning on travel time reliability, congestion, emissions, and energy consumption have been shown for homogenous roadway segments. However, the transportation system consists of inhomogeneous segments, and understanding the full impacts of platooning requires investigation in a realistic setup. One of the main reasons for inhomogeneity is speed limit fluctuations. Speed limit changes frequently throughout the transportation network, due to safety-related considerations (e.g., changes in geometry and workzone operations) or congestion management schemes (e.g., speed harmonization systems). In the current transportation systems with human-driven vehicles, these speed drops can potentially result in shockwave formation, which can cause travel time unreliability. Automated vehicles, however, have the potential to prevent shockwave formation and propagation and, therefore, enhance travel time reliability. Accordingly, this study presents a constant time headway strategy for automated vehicle platooning to ensure accurate tracking of any velocity profile in the presence of speed limit fluctuations. The performance of the presented platooning strategy is compared with Gipps’ car-following model and intelligent driver model, as representatives of regular non-automated vehicles. Simulation results show that implementing a fully autonomous system prevents shockwave formation and propagation, and enhances travel time reliability by accurately tracking the desired velocity profile. Moreover, the performance of platoons of regular and automated vehicles is investigated in the presence of a speed drop. The results show that as the market penetration rate of automated vehicles increases, the platoon can track the velocity profile more accurately.

Impacts analysis of car following models considering variable vehicular gap policies

Due to the important roles playing in the vehicles’ adaptive cruise control system, variable vehicular gap polices were employed to full velocity difference model (FVDM) to investigate the traffic flow properties. In this paper, two new car following models were put forward by taking constant time headway(CTH) policy and variable time headway(VTH) policy into optimal velocity function, separately. By steady state analysis of the new models, an equivalent optimal velocity function was defined. To determine the linear stable conditions of the new models, we introduce equivalent expressions of safe vehicular gap, and then apply small amplitude perturbation analysis and long terms of wave expansion techniques to obtain the new models’ linear stable conditions. Additionally, the first order approximate solutions of the new models were drawn at the stable region, by transforming the models into typical Burger’s partial differential equations with reductive perturbation method. The FVDM based numerical simulations indicate that the variable vehicular gap polices with proper parameters directly contribute to the improvement of the traffic flows’ stability and the avoidance of the unstable traffic phenomena.

Neural Adaptive Sliding-Mode Control of a Vehicle Platoon Using Output Feedback

This paper investigates the output feedback control problem of a vehicle platoon with a constant time headway (CTH) policy, where each vehicle can communicate with its consecutive vehicles. Firstly, based on the integrated-sliding-mode (ISM) technique, a neural adaptive sliding-mode control algorithm is developed to ensure that the vehicle platoon is moving with the CTH policy and full state measurement. Then, to further decrease the measurement complexity and reduce the communication load, an output feedback control protocol is proposed with only position information, in which a higher order sliding-mode observer is designed to estimate the other required information (velocities and accelerations). In order to avoid collisions among the vehicles, the string stability of the whole vehicle platoon is proven through the stability theorem. Finally, numerical simulation results are provided to verify its effectiveness and advantages over the traditional sliding-mode control method in vehicle platoons.

Third-order safe consensus of heterogeneous vehicular platoons with MPF network topology: Constant time headway strategy

In this paper the problem of centralized control of a platoon of non-identical vehicles under constant time headway strategy (CTHS) is investigated for multi predecessors following (MPF) topology. A centralized neighbor based linear control law using relative position and velocity is considered for each vehicle. Due to communication and parasitic delays and time-varying network topology, the closed-loop dynamics of platoon is in the form of a multiple delayed switched linear system. New approaches are developed to perform the internal stability analysis of one-dimensional heterogeneous vehicular platoons. Afterwards, sufficient conditions assuring the string stability of a platoon under MPF topology are obtained by presenting a new theorem. In continuance of the paper, some conditions on control parameters guaranteeing safety of the platoon in an emergency braking maneuver are presented through a new theorem. Several simulation results are provided to show the effectiveness of the proposed methods.

Distributed Adaptive Sliding Mode Control Strategy for Vehicle-Following Systems With Nonlinear Acceleration Uncertainties

This paper investigates the distributed adaptive control problems for nonlinear vehicle-following systems subject to nonlinear acceleration uncertainties involving vehicle acceleration disturbances, wind gusts, and parameter uncertainties. It is worth mentioning that the acceleration of the leader in most existing studies is always assumed to be zero or constant; the evolution of the leader in this paper may be subject to some unknown bounded input. Distributed adaptive control strategies based on an integral sliding mode control (ISMC) technique are proposed to maintain a rigid formation for a string of vehicle platoon in one dimension. First, distributed adaptive control based on traditional constant time headway (TCTH) policy under the assumption that the initial spacing and velocity errors are zero is developed to guarantee that all spacing errors are uniformly ultimately bounded and that the string stability of the whole vehicle platoon is also satisfied. Then, a modified constant time headway (MCTH) policy is proposed to remove the assumption of zero initial spacing and velocity errors and simultaneously effectively decrease the intervehicle spacing (i.e., increase the traffic density), making them nearly equal to those by using the constant spacing (CS) policy. Adaptive compensation terms without requiring a prior knowledge of upper bounds of the uncertainties are constructed to compensate for the time-variant effects caused by nonlinear acceleration uncertainties. Finally, numerical simulation results show the validity and advantages of the proposed policy up to a significant higher traffic density.

Developing a Distributed Consensus-Based Cooperative Adaptive Cruise Control System for Heterogeneous Vehicles with Predecessor Following Topology

Connected and automated vehicle (CAV) has become an increasingly popular topic recently. As an application, Cooperative Adaptive Cruise Control (CACC) systems are of high interest, allowing CAVs to communicate with each other and coordinating their maneuvers to form platoons, where one vehicle follows another with a constant velocity and/or time headway. In this study, we propose a novel CACC system, where distributed consensus algorithm and protocol are designed for platoon formation, merging maneuvers, and splitting maneuvers. Predecessor following information flow topology is adopted for the system, where each vehicle only communicates with its following vehicle to reach consensus of the whole platoon, making the vehicle-to-vehicle (V2V) communication fast and accurate. Moreover, different from most studies assuming the type and dynamics of all the vehicles in a platoon to be homogenous, we take into account the length, location of GPS antenna on vehicle, and braking performance of different vehicles. A simulation study has been conducted under scenarios including normal platoon formation, platoon restoration from disturbances, and merging and splitting maneuvers. We have also carried out a sensitivity analysis on the distributed consensus algorithm, investigating the effect of the damping gain on convergence rate, driving comfort, and driving safety of the system.

Distributed adaptive control for vehicular platoon with unknown dead‐zone inputs and velocity/acceleration disturbances

SummaryThis paper is focused on designing a distributed adaptive control scheme for a vehicular platoon with unknown bounded velocity/acceleration disturbances and unknown nonlinear dead‐zone inputs. Our aim is to design distributed adaptive controllers based on integral sliding mode control techniques that guarantee practical exponential convergence (i.e., exponential stability of an arbitrarily small neighborhood of zero) of the spacing errors and the string stability of the whole vehicular platoon. The contributions of this paper are that: (i) based on a modified constant time headway policy, the whole vehicular platoon is guaranteed to have string stability despite dead zone inputs; (ii) adaptive compensation terms are constructed to compensate for the time‐variant effects caused by unknown bounded velocity/acceleration disturbances, and unknown dead zone inputs; (iii) an efficient numerical method for avoiding the singularity problem of the control law is also proposed. Numerical simulation results show the validity and advantages of the proposed method are significantly higher traffic density and string stability. Copyright © 2016 John Wiley & Sons, Ltd.

Distributed Adaptive Integrated-Sliding-Mode Controller Synthesis for String Stability of Vehicle Platoons

This paper presents a distributed finite-time adaptive integral-sliding-mode (ISM) control approach for a platoon of vehicles consisting of a leader and multiple followers subjected to bounded unknown disturbances. In order to avoid collisions among the vehicles, control protocols have to be designed to ensure string stability of the whole vehicle platoon. First, the constant time headway (CTH) policy known to improve string stability is applied to the case of zero initial spacing errors. Contrary to requiring zero initial spacing and zero initial velocity errors simultaneously in existing methods based on constant spacing (CS) policy, initial velocity errors here are not required to be zero. Then, since string stability condition can fail at the initial conditions, a modified CTH policy is constructed to overcome string instability caused by nonzero initial spacing errors. Moreover, the proposed adaptive ISM control schemes can be implemented without the requirement that the bounds of the disturbances be known in advance. In addition, one effective method is proposed to reduce the chattering phenomenon caused by the indicator function. Finally, simulation results are included to demonstrate its effectiveness and advantages over existing methods.

Design of the time-gap-dependent robust headway control algorithm for ACC vehicles

A robust fuzzy headway control algorithm based on the constant time headway (CTH) model for adaptive cruise control (ACC) vehicles is developed. Considering the possible adjustment of the time gap (TG) by a driver after the activation of ACC, inter-vehicle kinematics is established by using a Takagi-Sugeno fuzzy model with the TG as the premise variable. A robust headway controller based on the model is designed by using the Lyapunov function approach. Control input saturation is considered in the design of the controller. Furthermore, the initial conditions of transitional manoeuvres from the velocity control mode to the distance control mode are computed on the basis of inter-vehicle kinematics. The designed algorithm is verified in various operating conditions. Passenger comfort can be improved by the designed algorithm under the precondition of driving safety in the tuning processes of the TG. And the individual preferences of various drivers on ACC are achieved and acceptability is eventually improved.

A hybrid traffic flow model with considering the influence of adaptive cruise control vehicles and on-ramps

Recently, autonomous vehicles and the relevant studies have attracted much attention. Adaptive cruise control (ACC), which is a kind of cruise control system for vehicles, automatically adjusts the vehicle speed to maintain a safe distance from vehicles ahead. Since the vehicle with ACC (called ACC vehicles) is semi-autonomous, the performance of ACC vehicle must be quite different from that of manual vehicle. The characteristics of traffic flow with ACC vehicles should be carefully investigated, especially when the traffic system is a bit complicated, such as on-ramp system. The primary objective of this paper is to propose a traffic flow model to simulate the traffic flow with considering the influence of ACC vehicles and on-ramps. Based on the model proposed by Yuan in 2009 [Yuan Y M 2009 Ph. D. Dissertation (Hefei: University of Science and Technology of China)], a hybrid traffic flow model with considering the influence of ACC vehicles and on-ramps is developed. Considering the differences between ACC and manual vehicles, a car-following sub-model based on constant time headway principle is developed for ACC vehicles, while an MCD cellular automata sub-model is proposed for manual vehicles. Besides, a new parameter, , is introduced to show different psychologies of drivers when changing lane from on-ramp to main road. The lane-changing model for vehicles on-ramp is developed as well. At the end, numerical simulation is demonstrated to study the influence of ACC vehicles on traffic flow at on-ramp, and to reveal the influence of parameters on the proposed hybrid model (i.e., the length of merge area, the desired time headway of ACC vehicle and ) on model performance. The results of this paper are as follows. 1) When the ACC vehicles exist in a traffic system, the performance of traffic flow in a on-ramp area is improved: the influence of merged vehicles on main road is reduced, and the average speed and volume are increased. 2) The increase of ACC vehicles can help to alleviate traffic congestion in both congestion duration and scope aspects. 3) The newly proposed hybrid model is sensitive to the length of merge area lw, the desired time headway of ACC vehicle Hd and lane-changing psychology parameter : the decrease of Hd and the increase of can both improve the average speed and volume of traffic flow. In addition, when the volume of on-ramp is small, the speed and volume of main road can be improved by enlarging lw. When the volume of on-ramp is large, a small lw will be better for traffic flow.

Cyclic interconnection for formation control of 1-D vehicle strings

In this paper, we study a formation control scheme for a 1-D string of vehicles. Each member tracks the movement of its immediate predecessor but also the first vehicle tracks the position of the last member of the string. We discuss conditions for the stability of the full interconnected system and show that if a constant spacing policy is used, the stability of the system is lost after the string size exceeds a certain number depending on the model parameters (vehicles and controllers). Additionally, we study the use of a constant time headway spacing policy. If the associated time headway parameter is greater than a critical value, the interconnected system is stable and string stable for any string size. Finally, we show that if an independent leader vehicle is added to the formation and every follower has access to this leader position, the cyclic formation with a constant spacing policy can be made stable and string stable by appropriately selecting a design parameter.