A headway safety policy for automated highway operations

The maximum capacity, cost, and safety of an automated highway system are largely dependent on the selected headway policy, i.e., the specification of a minimum acceptable headway (as a function of speed) for mainline operations. Here a policy, designed to avert collisions due to "reasonable" lead-car decelerations, is presented and evaluated in the context of achieving high capacity (≥3600 vehicle/lane/hr) over a range of typical highway speeds-13.5 to 30 m/s (30.2 to 67.2 mi/h). This involved a detailed analysis to determine both the relationships between, and the requirements on, the seven parameters which are embedded in this policy. These pertain to systems-level operations, the capabilities of a vehicle's automatic control system, and the vehicle/ roadway interface. The trade-offs associated with safety, capacity, and cost (in the form of required future development efforts) are identified, and three general approaches to selecting parameters for an operational system are specified.     

A Hybrid Neuro-Fuzzy System for Adaptive Vehicle Separation Control

The primary purpose of this paper is to develop a robust adaptive vehicle separation control in the increasingly important roles of intelligent transportation system (ITS). A hybrid neuro-fuzzy system (HNFS) is proposed for developing the adaptive vehicle separation control to minimize the distance (headway) between successive cars. This hybrid system consists of two modules: a headway identification (prediction) module and a control decision module. Each of these modules is realized with a distinct neuro-fuzzy network that upgrades hierarchical granularity and reduces the complexity in the control system. Given the current headway and relative velocity between the two consecutive cars, the headway identification module predicts the headway of the next time instant. This identified headway, together with the desired velocity are input to the control decision module whose output is the actual acceleration/deceleration control output. The HNFS encapsulates the adaptive learning capabilities of a neural network into a fuzzy logic control framework to fine-tune the fuzzy control rules. On the other hand, rules derived initially from well-defined fuzzy phase plane accelerate the training of the neural network. Simulation results are very encouraging. It is observed that the headway decreases significantly without sacrificing speed. Furthermore, both stability and robustness of HNFS are demonstrated.     

Autonomous intelligent cruise control

Vehicle following and its effects on traffic flow has been an active area of research. Human driving involves reaction times, delays, and human errors that affect traffic flow adversely. One way to eliminate human errors and delays in vehicle following is to replace the human driver with a computer control system and sensors. The purpose of this paper is to develop an autonomous intelligent cruise control (AICC) system for automatic vehicle following, examine its effect on traffic flow, and compare its performance with that of the human driver models. The AICC system developed is not cooperative; i.e., it does not exchange information with other vehicles and yet is not susceptible to oscillations and “slinky” effects. The elimination of the “slinky” effect is achieved by using a safety distance separation rule that is proportional to the vehicle velocity (constant time headway) and by designing the control system appropriately. The performance of the AICC system is found to be superior to that of the human driver models considered. It has a faster and better transient response that leads to a much smoother and faster traffic flow. Computer simulations are used to study the performance of the proposed AICC system and analyze vehicle following in a single lane, without passing, under manual and automatic control. In addition, several emergency situations that include emergency stopping and cut-in cases were simulated. The simulation results demonstrate the effectiveness of the AICC system and its potentially beneficial effects on traffic flow     

Model-follower longitudinal control for automated guideway transit vehicles

An approach for the design of longitudinal control systems for automated transit vehicles using the vehicle-follower control concept is presented. It is shown that the spacing policy selected for system operations generates a dynamic model for ideal vehicle response during station keeping. The longitudinal control system should force the actual vehicle response to be as close to this model response as possible. Two model-following controller designs are discussed. In one design the command from the controller is acceleration, and in the other design the command from the controller is jerk. The acceleration- and jerk-limited dynamic response of both controllers is examined by the use of describing functions and by computer simulations.     

Programmable digital vehicle control system

The programmable digital vehicle control system or PDVCS is based upon the Intel 8080A microprocessor and is designed to replace the hardwired discrete components traditionally used in the on-board control of automated rapid transit vehicles. Although designed specifically for the advanced group rapid transit (AGRT) system under development by the Boeing Company, with funding by the Department of Transportation, the PDVCS can easily be adapted for use in any automated transit system. A breadboard PDVCS has been programmed to perform the basic AGRT longitudinal control system functions, including closed-loop emergency braking, and has been subjected to closed-loop laboratory testing. Prototype tachometers and a seventh-order nonlinear analog computer simulation of motor, brake, and vehicle dynamics were used to close the control loop for test purposes; command scenarios were input manually. The test results demonstrate the feasibility of microcomputers in on-board vehicle control and show their capability to meet the performance requirements associated with a short headway (3 s) system.     

Short station ramps for AGT systems

Automated guideway transit (AGT) systems often have off-line stations, so that cars can travel directly from an origin to a destination, bypassing the intervening stations. Trip time is reduced, and a more flexible overall management policy is possible. The disadvantage of off-line stations is that additional guideway is required for the station and its associated ramps. More guideway is expensive, both to build and because of the extra space required. Conventional practice has assumed that the ramps leading into and out of off-line stations should be long enough 1) to accelerate to line speed before entering the main guideway and 2) to leave the guideway before decelerating into the station. Careful analysis using a headway safety computer program shows that ramps usually do not have to be this long. Acceleration and deceleration can safely take place on the main guideway. Possible reductions in ramp length are presented for a range of systems characteristics, assuming a constant headway control policy. These are compared with simple reference solutions. It is concluded that acceleration ramps can usually be eliminated. Deceleration ramps can often be greatly shortened, particularly if main guideway headway is sufficient for successive cars to enter a station.     

Vehicle location system experiment

A vehicle location system concept which utilizes narrow-band-radio trilateration has been developed for use in command and control systems designed to dispatch mobile vehicles. A comprehensive system experiment was carried out in Schenectady, N.Y., designed to evaluate the system's performance in a severe radio multipath environment, and to evaluate the improvement in performanee realized by system design options developed to improve performance degradation of multipath, that is, redundant receiving stations and space diversity antennas. Experimental results from the system experiment show that although high instrumental precision can be realized by narrow-band-radio trilateration techniques, a severe multipath environment, such as the Schenectady area produces by surrounding hills and valleys, degrades the instrumental precision. The results also indicate that four receiving stations each having four space diversity antennas will improve performance yielding a total vehicle location error radius of 900 ft, which is standard deviation for the Schenectady area.     

A linear induction motor control system for magnetically levitatedcarrier system

An electromagnetic suspension system has been developed that cuts off electric power-collecting devices from a magnetically levitated vehicle. This system makes it possible to transport materials with no mechanical contact at all between the vehicle and ground facilities. A control system for linear induction motors used in the magnetically levitated carrier system is described. The system was developed to transport materials in an environment which must be kept free from even microscopic dust motes and trivial noise. The linear induction motor control method used for positioning a vehicle at the station is described along with several kinds of switches without any mechanical motion in the ground facilities. A supervisory control system for the magnetically levitated carrier system is also discussed     

Computer models for AGT system operations studies

The major functions, inputs, and outputs of the seven computer models developed during the Automated Guideway Transit (AGT) System Operations Studies (SOS) project are described. The models were designed to provide tools to enable the transportation community to analyze the operation of AGT systems in the complete spectrum of deployments. Three analytic models are described: the feeder system model, which determines the cost and service characteristics of the non-AGT components of the door-to-door trip; the system cost model, which calculates annual and life cycle costs and environmental impacts; and the system availability model, which calculates the impact of failures and recovery times on passenger and vehicle delays in the network. Four simulation models are described: the discrete event simulation model, which models individual trips and vehicles on AGT networks for a wide range of management algorithms, service policies, and network configurations; the system planning model, which models vehicle and passenger flows on AGT networks; the detailed station model, which models individual vehicle and passenger movement in a station; and the detailed operational control model, which is a time step simulation that models individual or strings of vehicles on links, merges, or intersections.     

An analysis of vehicle-to-infrastructure communications for non-signalised intersection control under mixed driving behaviour

Intersection control has an important role in the management of urban traffic to ensure safety, high traffic flow and to prevent congestion. Recently, a growing body of literature has been reported on the theme of non-signalised intersection control in which traffic lights are replaced with intelligent road side units. Data from several studies suggest that non-signalised control could reduce vehicle delays and fuel consumption significantly whilst ensuring safety. However, there is little published data on the impact of the mixed driving behaviour with human-driven vehicles and autonomous vehicles. This paper investigates the emerging role of connectivity and vehicle autonomy in the context of traffic control under the mixed driving behaviour scenario. The concepts of vehicle-to-infrastructure (V2I) communications and multi-agent systems are central to achieving a robust and reliable traffic-light-free intersection control. Comprehensive computer simulation results on a four-way intersection indicate over 96% reduced average vehicle delay and 37% less fuel consumption with the non-signalised control solution compared to the traffic light control. The outcome of this study offers some important insights into enabling cooperation between vehicles and traffic infrastructure via V2I communications, in order to make more efficient real-time decisions about traffic conditions, whilst ensuring a higher degree of safety.     

A study of automatic car following

Virtually all proposed vehicle control systems for highway automation must include a steady-state car-following mode. This mode was intensively investigated for various situations where headway and relative velocity inputs were used. In addition, a fundamental relationship between the flow capacity of an automated highway and the small-signal longitudinal response of a vehicle was investigated. The predictions obtained from mathematical models of various car-following modes were compared to those from full-scale tests. It was concluded that a linear mathematical representation of the longitudinal dynamics was valid, and thus it could be used for predictive purposes. Furthermore, it was verified that flow capacity on an automated highway is sharply limited by certain vehicle characteristics if headway feedback is used for vehicle control.     

High capacity personal rapid transit system developments

High capacity personal rapid transit (HCPRT) is a system concept which utilizes small, 4 to 6 passenger, vehicles at very short headways on exclusive guideway networks. The automatic operation of small vehicles at headways of 1 s or less presents a major technical problem which is amenable to a combination of design approaches. This paper explores the effect of basic parameters such as vehicle length, reaction time, emergency and failed vehicle deceleration rates, and emergency jerk rate on potential minimum operating headway. The results of this analysis are then discussed in the context of five HCPRT programs.     

Real-time vision-based tracking control of an unmanned vehicle

Recent advances in manufacturing automation have motivated vision-based control of autonomous vehicles operated in unattended factories, material handling processes, warehouse operations, and hazardous environment explorations. Existing vision-based tracking control systems of autonomous vehicles, however, have been limited in real-time applications due to slow and/or expensive visual feedback and complicated dynamics and control with nonholonomic constraints. This paper presents a practical real-time sion-based cking control system of an unmanned vehicle, ViTra. Unlike the conventional RS170 video-based machine vision systems, ViTra uses a DSP-based flexible integrated vision system (FNS) which is characterized by low cost, computational efficiency, control flexibility, and a friendly user interface.

In particular, this paper focuses on developing a framework for vision tracking systems, designing generic fiducial patterns, and applying real-time vision systems to tracking control of autonomous vehicles. A laboratory prototype vision-based tracking system developed at Georgia Institute of Technology permits the uniquely designed fiducial landmarks to be evaluated experimentally, the control strategy and the path planning algorithm derived in the paper to be validated in real-time, and the issues of simplifying nonlinear dynamics and dealing with nonholonomic constraints to be addressed in practice. Experimental results reveal interesting insights into the design, manufacture, modeling, and control of vision-based tracking control systems of autonomous vehicles.     

Nonlinear brake control for vehicle CW/CA systems

A brake control law for vehicle collision warning/collision avoidance (CW/CA) systems has been proposed in the paper. The control law has been designed for optimized safety and comfort. A solenoid-valve-controlled hydraulic brake actuator system for the CW/CA systems has been investigated. A nonlinear computer model and a linear model of the hydraulic brake actuator system have been developed. Both models were found to represent the actual system with good accuracy. Uncertainties in the brake actuator model have been considered in the design of the control law for the robustness of the controller. The effects of brake control on CW/CA vehicle response has been investigated via simulations. The simulations were performed using a complete nonlinear vehicle model. The results indicate that the proposed brake control law can provide the CW/CA vehicles with an optimized compromise between safety and comfort     

A Resilient and Scalable Flocking Scheme in Autonomous Vehicular Networks

Vehicular Ad hoc NETworks (VANET) is emerging as a highly promising technology, which aims to provide road safety, environment protection and personal-oriented services. The vehicle ad hoc wireless communications form an indispensable part of truly ubiquitous communications networking. VANET is formed by spontaneously moving autonomous vehicles with the self-organization and self-management capability. In this paper, we focus on the decentralized coordination of multiple unmanned vehicles such that they can freely move and adaptively cooperate in a complex environment. During this procedure, flocking is one of the key operations and requirements. Here, flocking refers to the formation and maintenance of a desired pattern by a group of mobile vehicles without collision during movement. We propose a resilient and scalable flocking scheme for a group of vehicles, which follows the leader–followers moving pattern. In the absence of obstacles, a collision avoidance algorithm is presented to maintain a desired distance among vehicles. This will ensure information completeness and is significant in certain mission critical situations without collision between a unmanned vehicle and its neighboring vehicles. In the presence of obstacles in an environment, this algorithm is able to avoid collision between a vehicle and its neighbor (either a neighboring vehicle or a neighboring obstacle). Theoretical proof has been presented to demonstrate the effectiveness and correctness of the algorithm to guarantee collision-free. In addition, with increasing number of vehicles, the performance of the proposed flocking scheme performs without increasing the processing overhead, which demonstrates the desirable scalability.     

A genetic technique for robotic trajectory planning

There are many multi-stage optimization problems that are not easily solved through any known direct method when the stages are coupled. For instance, the problem of planning a vehicle's control sequence to negotiate obstacles and reach a goal in minimum time is investigated. The vehicle has a known mass, and the controlling forces have finite limits. A genetic programming technique is developed that finds admissible control trajectories that tend to minimize the vehicle's transit time through the obstacle field. The immediate application is that of a space robot that must rapidly traverse around two or three dimensional structures via application of a rotating thruster or non-rotating on-off thrusters. (An air-bearing floor test-bed for such vehicles is located at the Marshal Space Flight Center in Huntsville, Alabama.) It appears that the developed method is applicable to a general set of optimization problems in which the cost function and the multi-dimensional multi-state system can be any non-linear functions that are continuous in the operating regions. Other applications include: the planning of optimal navigation pathways through a traversability graph, the planning of control input for underwater maneuvering vehicles which have complex control state-space relationships, the planning of control sequences for milling and manufacturing robots, the planning of control and trajectories for automated delivery vehicles, and the optimization of control for racing vehicles and athletic training in slalom sports.     

Modified Pulse-Adjustment Technique to Control DC/DC Converters Driving Variable Constant-Power Loads

Multiconverter-distributed DC architectures have been utilized for power distribution in many applications such as telecommunication systems, sea and undersea vehicles, an international space station, aircraft, electric vehicles, hybrid-electric vehicles, and fuel-cell vehicles, where reliability is of prime concern. The number of power-electronic converters (AC/DC, DC/DC, DC/AC, and AC/AC) in these multiconverter electrical power systems varies from a few converters in a conventional land vehicle, to tens of converters in an advanced aircraft, and to hundreds of converters in the international space station. In these advanced applications, power-electronic converters might need to have a tight output-voltage regulation. From the output perspective, this property is highly desirable. However, since power-electronic converters are efficient, tight regulation of the output makes the converter appear as a constant-power load (CPL) at its input side. Dynamic behavior of CPLs is equivalent to negative impedance and, therefore, can result in instability of the interconnected power system. In order to mitigate the instability of the power converters loaded by CPLs, this paper presents the pulse-adjustment digital control technique. It is simple and easy to implement in application-specific integrated circuits, digital-signal processors, or field-programmable gate arrays. Moreover, its dynamic response is fast and robust. Line and load regulations are simply achievable using this technique. Analytical, as well as simulation and experimental results of applying the proposed method to a DC/DC buck-boost converter confirm the validity of the presented technique.     

LIDAR Sensing for Vehicle Lateral Guidance: Algorithm and Experimental Study

This paper describes a new vehicle detection system based on a laser imaging, detection, and ranging (LIDAR) sensor, and conducts an experimental study to investigate the sensor's role in the current California PATH vehicle lateral guidance systems. The LIDAR sensor is installed on a controlled vehicle and it can measure the relative distance of the vehicle from a preceding vehicle, by scanning the horizontal plane with laser beams. Environmental clutter becomes the main challenge in data processing, when LIDAR tries to track the desired target. A probabilistic data association-based algorithm has been developed to solve this problem, which has been verified in real-time experiments using two Buick LaSabre vehicles. The experimental study also reveals the relation between the LIDAR outputs and the magnetic reference system widely used by the current PATH lateral control systems, and the results provide the guidelines on how this new sensor system may be used for vehicle lateral guidance     

Analysis of alert message propagation on the highway in VANET assuming Markovian vehicle arrival process

Vehicular ad hoc networks (VANETs) provide the infrastructure for the intelligent transportation system (ITS). The number of vehicles that are capable of communicating with each other through VANET is increasing. In this paper, we provide several analytical results regarding the message propagation on the highway in VANET. In our scenario, there is a stationary message source (i.e., alert messages are generated at an accident). Vehicles can receive the message and get informed when they reach the radio transmission range of the message source or another informed vehicle. Most papers published on the analysis of message propagation assume that the inter arrival times between vehicles follow a Poisson process; there are very few results available with more general traffic model. In this paper, we show that the Poisson process is not always suitable for modeling vehicle traffic. Instead of the Poisson process, we propose to use the more general Markovian arrival process (MAP) to model the vehicle headway times and derive the probability that the message propagates beyond a certain distance from the accident under this traffic assumption. Through several numerical examples, we demonstrate how much the statistics of the vehicle arrival process impacts the message propagation distance.     

Second order sliding mode control of vehicles with distributed collision avoidance capabilities

Recent research has shown that the longitudinal control of platoons of vehicles is appropriate to improve the traffic capacity of road networks while maintaining the safety distance between vehicles. This paper investigates the possibility of reducing the number of accidents involving pedestrians or other vulnerable road users (VRUs), like cyclists and motorcyclists, by providing the control systems of the vehicles of the platoon with some collision detection and avoidance capabilities. The control system proposed in this paper allows to maintain a desired distance from the preceeding vehicle, and, as a novelty with respect to other proposals, to avoid the collision with VRUs present on the road. The proposed control scheme is realized by means of a supervisor, which makes the decision on which is the appropriate current control mode for each controlled vehicle, and manages the switches among low-level controllers. The adopted control technique is the so-called sliding mode control methodology, which is particularly suitable to deal with the uncertainties and disturbances typical of automotive applications.