Showing papers on "Headway published in 1997"

Human Factors Field Evaluation of Automotive Headway Maintenance/Collision Warning Devices

Abstract: Three on-road studies were conducted to determine how headway maintenance and collision warning displays influence driver behavior. Visual perspective, visual perspective with a pointer, visual perspective combined with an auditory warning, discrete visual warning, and discrete auditory warning were assessed during both coupled headway and deceleration events. Results indicate that when drivers are provided with salient visual information regarding safe headways, they utilize the information and increase their headway when appropriate. Auditory warnings were less effective than visual warnings for increasing headways but may be helpful for improving reaction time during events that require deceleration. Drivers were somewhat insensitive to false alarm rates, at least during short-term use. Finally, and most important, driver headway maintenance increased by as much as 0.5 s when the appropriate visual display was used. However, a study to investigate the longterm effects of such displays on behavior is strongly recommended prior to mass marketing of headway maintenance/collision warning devices.

Assessment of roadway capacity estimation methods

Abstract: Capacity is a central concept in roadway design and traffic control. Estimation of empirical capacity values in practical circumstances is not a trivial problem; it is very difficult to define capacity in an unambiguous manner. Empirical capacity estimation for uninterrupted roadway sections has been studied. Headways, traffic volumes, speed, and density are traffic data types used to identify four groups of capacity estimation methods. Aspects such as data requirement, location choice, and observation period were investigated for each method. The principles of the different methods and the mathematical derivation of roadway capacity are studied and discussed. Among the methods studied are the headway distribution approaches, the bimodal distribution method, the selected maxima, and the direct probability method. Of the methods based on traffic volume counts, the product limit method is recommended for practical application because of sound underlying theory. An example of the application of this promisin...

Intelligent cruise control field operation test

Abstract: This interim document reports on a cooperative agreement between NHTSA and UMTRI entitled Intelligent Cruise Control (ICC) Field Operational Test (FOT). The overarching goal of the work is to characterize safety and comfort issues that are fundamental to human interactions with an automatic headway keeping system. This report summarizes the status of the FOT and presents preliminary results and findings deriving from the testing activities now in progress. It describes work done to prepare and instrument a fleet of 10 passenger cars with infrared ranging sensors, headway control algorithms, and driver interface units as needed to provide an adaptive cruise control (ACC) functionality. The vehicles have been given to lay drivers to use for two weeks as their personal cars. Based upon data from 35 drivers, objective and subjective results support the following preliminary observations: ACC driving is reported to be comfortable and is perceived as stress relieving. The kinesthetic sensation of ACC-induced deceleration was often cited by drivers as a vigilance-enhancing cue, perhaps implying a safety benefit. Drivers appear to learn how to use ACC quickly and to converge on a strategy that meshes with their driving style. The data contain a natural type of "bias" by which manual driving appears riskier than ACC driving in part because denser, more conflict-laden, traffic induces drivers to turn the ACC system off. Under virtually all conditions in which ACC is engaged, drivers choose (and the system provides) headway distances that are greater than those seen when the same person drives manually. ACC driving results in fewer "near approaches" to the preceding vehicle than does manual driving. Headway-keeping behavior differs markedly with driver age. Younger drivers are typically more aggressive, operating at shorter headways. Given the properties of the ACC system being studied, a minimal impact on the accident record would be expected from observations to date. A major element of this expectation derives from the drivers' choice to use ACC only in rather benign traffic environments. When completed, the FOT is expected to present findings based on results from over 100 drivers/participants.

The format and presentation of collision warnings

Abstract: This paper reports on two studies focusing on the design of collision avoidance headway displays. The first study aims at examining interface issues relating to the headway information to drivers. It investigates integrated visual and auditory warnings. The purpose of the second study is to examine two particular factors that may affect drivers' braking responses in their use of an experimental Collision Avoidance System. It looks at the effects of both the absolute speeds of the target and following vehicle and the relative speed differences between the two vehicles.

The 1997 automated highway free agent demonstration

Abstract: In August 1997, the US National Automated Highway System Consortium (NAHSC) presented a proof of technical feasibility demonstration of automated driving. It took place on I-15, in San Diego, California. Members of the consortium demonstrated many different functions: vision-based road following, following magnetic nails, following a radar reflective strip, radar-based headway maintenance, ladar-based headway maintenance, evolutionary systems, close vehicle following (platooning), cooperative maneuvering, obstacle detection and avoidance, mixed automated and manual driving, mixed automated cars and buses, and semi-automated maintenance. CMU led the effort to build one of the seven demonstration scenarios, the Free Agent Demonstration (FAD). The FAD involved two fully automated cars, one partially automated car, and two fully automated city buses. The scenario demonstrates lane entry, speed and headway control, lane following, lane changing, obstacle detection, and cooperative maneuvers. This paper describes the free agent demonstration itself, the technology that made the demonstration possible, and the future work to analyze the feasibility of turning the demonstration system into a practical prototype.

Operational Benefits of Electronic Toll Collection: Case Study

Abstract: This paper reports the improvements in traffic operations at the electronic toll collection plazas of the Orlando-Orange County Expressway Authority. Service time, vehicle arrival times, and departure times, as well as vehicle counts were collected “before” and “after” the installation of automatic vehicle identification technology known as E-PASS. The findings indicate that, for the dedicated E-PASS lane, the measured capacity has tripled, the service time has decreased by five seconds per vehicle, the average queuing delay has decreased by one minute per vehicle, the maximum queuing delay has decreased by 2.5–3 minutes per vehicle, and the total queuing delay has decreased by 8.5–9.5 vehicle-hours per morning peak hour for that lane. Also, variability in the headway has been reduced significantly in the dedicated E-PASS lane. Capacity, headway, and service times of the mixed (manual/E-PASS or automatic/E-PASS) lanes did not change significantly. However, arrivals have shifted to the dedicated E-PASS lan...

The microscopic traffic simulation model mixic 1.3

Abstract: The MICroscopic model for Simulation of Intelligent Cruise control (MIXIC) 1.3 was developed for studying the Autonomous Intelligent Cruise Control (AICC) impacts on a number of consecutive motorway stretches. MIXIC 1.3 contains detailed submodels describing drivers, vehicles, assisting systems and their interfaces. The model has been filled for 4 driver and 4 vehicle types. Passenger cars may be equipped with AICC. Drivers of these cars can switch their AICC on or off depending on the prevailing traffic conditions. This interaction model is motivated by the fact that first generation AICC systems are expected to have a limited deceleration range, and must be overruled by the driver if strong decelerations are required. The MIXIC output ranges from the possibility of recording vehicle/driver combinations to the measurement of aggregated traffic quantities and the occurrence and severity of shock waves. The model offers the possibility of narrowing situations and dedicated lanes for AICC vehicles. (A) See also IRRD 874631 and 898629.

Particle-hopping models of vehicular traffic: Distributions of distance headways and distance between jams

Abstract: We calculate the distribution of the distance headways (i.e., the instantaneous gap between successive vehicles) as well as the distribution of instantaneous distance between successive jams in the Nagel-Schreckenberg (NS) model of vehicular traffic. When the maximum allowed speed, Vmax, of the vehicles is larger than unity, over an intermediate range of densities of vehicles, our Monte Carlo (MC) data for the distance headway distribution exhibit two peaks, which indicate the coexistence of “free-flowing” traffic and traffic jams. Our analytical arguments clearly rule out the possibility of occurrence of more than one peak in the distribution of distance headways in the NS model when Vmax=1 as well as in the asymmetric simple exclusion process. Modifying and extending an earlier analytical approach for the NS model with Vmax=1, and introducing a novel transfer matrix technique, we also calculate the exact analytical expression for the distribution of distance between the jams in this model; the corresponding distributions for Vmax > 1 have been computed numerically through MC simulation.

Driver car following behavior under test track and open road driving condition

Abstract: This paper presents the results of an experiment which focused on driver behavior in car following tasks. The research was motivated by a desire to understand the dynamics of driver headway control as a guide for setting the automatic control characteristics of an Adaptive Cruise Control (ACC) system. Experiments are described, and the results describe data analysis, dynamic coupling and control and headway distributions.

System wide adaptive ramp metering (swarm)

Abstract: This paper presents the development of a centrally controlled segmented system wide adaptive ramp metering (SWARM) system. This adaptive ramp metering approach includes the use of two algorithms, SWARM 1 and SWARM 2. The development of this system was initiated by the California Department of Transportation's (Caltrans) Freeway Traffic Management System in the Los Angeles area. One of the largest systems in the world, it encompasses over 30,000 traffic detectors and 1,200 ramp meters. Currently, ramp metering operations are based on time-of-day tables that are periodically updated and an automatic local mainline responsive algorithm. The SWARM system operates on a two tier approach. SWARM 1 consists of forecasting and a centrally controlled system wide apportionment of ramp metering rates across specific segments of the entire freeway network. It is based on real time control, thereby offering a proactive approach to congestion. Density is the control parameter of the SWARM 1 algorithm as density is directly related to congestion. Forecasting is accomplished by using the Kalman Filter, a mathematical technique that takes into account noise in the data to produce a non-liner forecast. SWARM 2 is composed of two separate algorithms. Which algorithm is used to determine the metering rate depends on the particular data available. SWARM 2a, which was developed by Caltrans District 12, is based on headway theory and uses a density function to compute local metering rates. SWARM 2b is based on the computation of the number of vehicles stored in a defined section of freeway. Both SWARM 1 and SWARM 2 are continuously calculating potential metering rates and the high level SWARM system implements the most restrictive of the two rates. Following the detailed description of the theory supporting SWARM 1 and SWARM 2 is an explanation of the Data Quality Requirements for the algorithms. Data Quality Requirements include: Failure Management, Data Enhancement and Constraints. Data enhancements include: sources of error, data normalization and dynamic saturation determination. Constraints include: unrestricted entries, deficient or missing data, manual overrides, minimum metering rates, time of day rates and local queueing strategies. Final implementation and integration with Caltrans District 12 is scheduled for June of 1997. Testing, calibration and evaluation is scheduled for early 1997. Caltrans District 7 integration is also scheduled for 1997. Historical data sets have been utilized to test the forecasting algorithm and have produced positive results. Forecasts follow actual density trends toward saturation well in advance of reaching saturation density.

Particle-hopping Models of Vehicular Traffic: Distributions of Distance Headways and Distance Between Jams

Abstract: We calculate the distribution of the distance headways (i.e., the instantaneous gap between successive vehicles) as well as the distribution of instantaneous distance between successive jams in the Nagel-Schreckenberg (NS) model of vehicular traffic. When the maximum allowed speed, $V_{max}$, of the vehicles is larger than unity, over an intermediate range of densities of vehicles, our Monte Carlo (MC) data for the distance headway distribution exhibit two peaks, which indicate the coexistence of "free-flowing" traffic and traffic jams. Our analytical arguments clearly rule out the possibility of occurrence of more than one peak in the distribution of distance headways in the NS model when $V_{max} = 1$ as well as in the asymmetric simple exclusion process. Modifying and extending an earlier analytical approach for the NS model with $V_{max} = 1$, and introducing a novel transfer matrix technique, we also calculate the exact analytical expression for the distribution of distance between the jams in this model; the corresponding distributions for $V_{max} > 1$ have been computed numerically through MC simulation.

Collision avoidance behavior of unalerted drivers using a front-to-rear-end collision warning display on the Iowa driving simulator

Abstract: This study investigated whether drivers who operate a vehicle equipped with a front-to-rear-end collision warning system can avoid crashing when a lead vehicle brakes at its maximum potential (e.g., -0.85 g). Drivers in the experimental condition drove a 1993 General Motors Saturn mounted on the Iowa Driving Simulator's six-degree-of-freedom motion base. The simulator cab was equipped with a collision warning display that provided a primary auditory warning and secondary visual warning based on a time-to-collision algorithm between the subject's vehicle and the lead vehicle. Two headway distances were tested (2.7 sec and 3.2 sec). The collision avoidance performance of subject drivers was compared to the behavior of drivers in a baseline condition where no collision warning display was present. Relative to the baseline condition, results indicate that drivers using the collision warning display (a) showed significantly fewer crashes in the shorter headway condition, (b) collided with the lead vehicle at s...

A review on the process to estimate the Cowan M3 headway distribution parameters

Abstract: The paper discusses the evaluation of the parameters for Cowan's M3 headway distribution for the express purpose of being used in a gap acceptance situation, although the remarks are pertinent to other situations and to other headway distributions.

Crash reduction with an advance brake warning system: a digital simulation

Abstract: A digital Monte Carlo-type simulation was used to evaluate the effectiveness of an advance brake warning system (ABWS) in reducing rear-end collisions. The ABWS we evaluated activates the brake lights in response to rapid release of the gas pedal, which is characteristic of emergency braking. This reduces the lag in the onset of the brake light by the movement time from the gas pedal to the brake pedal. Using empirical distributions of driver perception reaction time and movement times, it was shown that the ABWS is most effective in preventing collisions on dry roads whenever the headway between vehicles decreases to 1.0 s or less. Vehicle speed was not a significant factor in crash prevention or severity reduction.

Modeling and Estimation of Headway Distributions

Abstract: A simple analysis to derive Branston's generalized queueing model for (time-) headway distributions is presented. It is assumed that the total headway is the sum of two independent random variables: the empty zone and the free-flowing headway. The parameters of the model can be used to examine various characteristics of both the road (e.g., capacity) and driver-vehicle combinations (e.g., following behavior). Furthermore, the model can be applied to vehicle generation in microscopic simulation models and to safety analysis. To estimate the different parameters in the model, a new estimation method is proposed. This method, which was developed on the basis of Fourier-series analysis, was successfully applied to measurements collected on two-lane rural roads. The method was found to be both computationally less demanding and more robust than traditional parameter techniques procedures, such as maximum likelihood. In addition, the method provides more accurate results. Parameters in the model were examined with the developed estimation method. Estimates of these parameters at a specific period and a specific measurement location were to some extent transferable to other periods and locations. Application of the method to road capacity estimation is discussed.

Brake assist system

Abstract: PROBLEM TO BE SOLVED: To perform a brake assisting function appropriately by applying a brake pressure higher than that generated through depression of the brake pedal operated by a driver in response to the determination that the driver's vehicle is approaching the vehicle running ahead too close based on the distance between those vehicles less than the threshold value. SOLUTION: A control unit 29 detects the headway distance between the running vehicle and the object existing in front thereof and detects the speed of the running vehicle, which can be used to calculate the relative speed. Based on the relative speed, the braking distance is calculated. A threshold value is obtained by adding the allowance distance and the calculated braking distance. If the present headway distance is less than the threshold value, it is determined that the vehicle has been approaching the object ahead too close. Then, the control is executed to drive the solenoid valve of the negative booster 25 such that the braking pressure higher than that generated through depression of the brake pedal by the driver. As a result, the brake assist control can be appropriately performed.

Trip Assignment Model for Timed-Transfer Transit Systems:

Abstract: A trip assignment model for timed-transfer transit systems is presented. Previously proposed trip assignment models focused on uncoordinated transit systems only. In timed-transfer transit systems, routes are coordinated and scheduled to arrive at transfer stations within preset time windows. Thus, passengers at coordinated operations terminals may face a choice among simultaneously departing buses serving alternative routes (unlike the case for uncoordinated operations terminals, where passengers generally board the first vehicle to arrive). A general trip assignment model is proposed that applies different assignment rules for three types of transfer terminals: uncoordinated operations terminals, coordinated operations terminals with a common headway for all routes, and coordinated operations terminals with integer-ratio headways for all routes. In addition, the care of missed connections at transfer terminals (due to vehicles arriving behind schedule) is accounted for. The model has been implemented in...

Cruise control system

Abstract: A cruise control system for a motor vehicle includes a sensor for monitoring a target vehicle moving in front of the equipped vehicle, a sensor for monitoring the speed of the equipped vehicle and a sensor for monitoring steering manoeuvres of the equipped vehicle, the cruise control system controlling the throttle and brake systems of the vehicle to control the speed of the vehicle. The cruise control system is switchable between a cruise mode in which it will maintain a set cruising speed when the path in front of the vehicle is clear and a follow mode in which it will maintain a preset headway with a target vehicle in front of the equipped vehicle. The system is switched from the cruise mode to the follow mode when a target vehicle moves inside the preset headway, the system switching from the follow mode to the cruise mode when the target vehicle is lost or moves outside a preset headway. When switching from the follow mode to the cruise mode, the cruise control system applies a resume acceleration to accelerate the equipped vehicle back to the set cruising speed, the resume acceleration rate being adjusted as a function of steering manoeuvres carried out by the equipped vehicle.

Millimeter-wave dual mode radar for headway control in IVHS

Abstract: In intelligent vehicle and highway systems (IVHS), lateral and headway vehicle control is used to maintain stable driving. Headway control keeps the controlled vehicle an appropriate distance from vehicles directly ahead. Each vehicle needs to have an obstacle detection system installed to monitor distances to the preceding vehicle and its relative speed. In the future, headway control systems for consumer use must be cheap and capable of operating in all environmental conditions. To enable such equipment to be built, a dual mode millimeter-wave radar has been proposed. It would be able to operate in both radar mode, in which it would measure the distance to the leading vehicle, and in communication mode, in which it would exchange data with a vehicle ahead of it. By operating in two modes alternately, the dual mode radar can provide the headway control system with all the data needed to control the distances to the leading vehicles, their speeds, acceleration conditions, and the leading vehicle's steering angle and brake signal. The data can then be used for stable control of the vehicles. This paper describes the concept of the dual mode radar system and the results of the experiments undertaken.

An experimental design for studying how driver characteristics influence headway control

Abstract: The sample of drivers, representing a random sample of the population of licensed drivers in southeastern Michigan, was selected according to a design that stratified the population by age and prior use of conventional cruise control. An essential element of the design was that each driver's operation with adaptive cruise control (ACC) is compared with the same individual's driving in the "manual" mode of vehicle operation. The experimental design was based, in part, on findings from previous research projects. Specifically, the independent variables of participant age and conventional cruise control usage were previously found to influence both objective and subjective dependent measures. The paper delineates the experimental design and outlines its execution.

An exponential relationship for the proportion of free vehicles on arterial roads

Abstract: The proportion of free vehicles on a road link is dependent on the geometry of the road link and the presence of intersections along the link. This paper details the investigation of the proportion of free vehicles as a function of the link geometry. It is necessary to define the effects of the link geometry before the effect of intersections on the headway distribution can be incorporated. Current methods for describing the proportion of free vehicles on a road link predominantly use linear relationships with the vehicle flow rate. An exponential relationship has been examined and found to be better suited to the modelling of the proportion of free vehicles than the existing linear relationships. In modelling the flow in each lane, the characteristics of the traffic flow were found to be dependent on the lane type being modelled. The kerb lane sustained a higher proportion of free vehicles than the median lane for similar flow rates. This finding is significant in the analysis of priority intersections. The difference is attributed to driver behaviour and is related to the expected ease of overtaking. Using these results the proportion of free vehicles is described as a function of the lane type, lane width and the vehicle flow rate through the use of exponential relationships. The influence of intersections upon the characteristics of the traffic flow can then be incorporated by describing the effect of the proportion of free vehicles on the road link.

Tests Characterizing Performance of an Adaptive Cruise Control System

Abstract: This paper describes methods for characterizing the headway control performance of adaptive cruise control (ACC) systems. The inputs to the test are the speed of the preceding vehicle. Results of the tests are based upon measurements of range, range rate, velocity transmission shift commands,, and velocity commands. Numerical performance measures are derived from these data and are used to characterize system performance quantitatively.

Optimum Bus Headway for Preemption: A Simulation Approach

Abstract: Preemption techniques are designed to provide preferential treatment for buses at signalized intersections. A preemption strategy, if properly designed, can provide continuous green phases for buses at successive intersections, thereby reducing travel times and delays along the bus route. However, the length of delay incurred by all the vehicles in the system may be affected by the different bus headways under preemption operation. Unfortunately, no formal technique is available to assess the cumulative delay consequences of bus headways. The application of a simulation model, NETSIM, to test the effect of different headways is presented. NETSIM was selected because it can microscopically simulate vehicular movements on a street network and because an animation feature within NETSIM is available that allows the user to track an individual vehicle from the source to the sink. A major bus route in Ann Arbor, Michigan, was used as the experiment site. The major conclusions are that NETSIM can generate delay data at various levels of aggregation (e.g., link, node, and route) that can be used to assess the operational consequences of bus headways under preemption conditions. For the volume levels studied in the project, the savings in delay along the bus route resulting from preemption appears to be a good measure for determining the optimum headway.

Cruise control system for motor vehicles

Abstract: Cruise control system for a vehicle includes a sensor for monitoring the speed of the vehicle, a sensor for monitoring the range of vehicles moving in front of the equipped vehicle, switch means for manually selecting a cruising speed, switch means for manually selecting a headway which controls the separation between the equipped vehicle and a vehicle moving in front of the equipped vehicle and means for switching the cruise control system on and off. The switch means for selecting the headway is manually adjustable between a minimum value and a maximum value. Automatic switch means is provided for switching the cruise control system off when the vehicle is stopped, the headway being automatically switched to a maximum value when the cruise control system is switched on.

Cruise control system with vehicle following mode

Abstract: A cruise control system for a motor vehicle includes a sensor (14) for monitoring a target vehicle (42) moving in front of the equipped vehicle (40), a sensor (12) for monitoring the speed of the equipped vehicle (40) and a sensor (16) for monitoring steering manoeuvres of the equipped vehicle (40), the cruise control system controlling the throttle and brake systems of the vehicle (40) to control the speed of the vehicle (40). The cruise control system is switchable between a cruise mode in which it will maintain a set cruising speed when the path in front of the vehicle (40) is clear and a follow mode in which it will maintain a preset headway with a target vehicle (42) in front of the equipped vehicle (40). The system is switched from the cruise mode to the follow mode when a target vehicle (42) moves inside the preset headway, the system switching from the follow mode to the cruise mode when the target vehicle (42) is lost or moves outside a preset headway. When switching from the follow mode to the cruise mode, the cruise control system applies a resume acceleration to accelerate the equipped vehicle (40) back to the set cruising speed, the resume acceleration rate being adjusted as a function of steering manoeuvres carried out by the equipped vehicle (40).

Vehicle Following Control Design for Automated Highway Systems

Abstract: Automatic vehicle following is an important feature of a fully or partially automated highway system (AHS). The on-board vehicle control system should be able to accept and process inputs from the driver, the infrastructure and other vehicles, perform diagnostics and provide the appropriate commands to actuators so that the resulting motion of the vehicle is safe and compatible with the AHS objectives. The purpose of this paper is to design and test a vehicle control system in order to achieve full vehicle automation in the longitudinal direction for several modes of operation, where the infrastructure manages the vehicle following. These modes include autonomous vehicles, cooperative vehicle following and platooning. The vehicle control system consists of a supervisory controller that processes the inputs from the driver, the infrastructure, other vehicles and the on-board sensors and sends the appropriate commands to the brake and throttle controllers. In addition, the controller makes decisions about normal, emergency and transition operations. Simulation results of some of the basic vehicle following maneuvers are used to verify the claimed performance of the designed controllers. Experiments on 1-15 that demonstrate the performance of the throttle controller with and without vehicle-to-vehicle communications in an actual highway environment are also included.

Intelligent systems for priority at traffic signals in london: the income project

Abstract: Bus priority using selective detection has now been implemented at many isolated and coordinated traffic signals in London, including junctions under SCOOT UTC control. System evolution is now progressing to encompass new communications systems, advanced control strategies and integration. This paper describes this evolutionary process within the European Commission DGVII project INCOME. Summary results are presented from active bus priority field trials in fixed time and traffic responsive UTC. A new architecture for using Automatic Vehicle Location (AVL) to provide bus-specific priority levels according to individual bus requirements is then described, including off-line evaluation of associated headway algorithms. The paper concludes with an outline of other individual and integrated applications in INCOME to help buses in London. (A) For the covering abstract, see IRRD 490001.

Development of rear-end collision avoidance system

Abstract: RCAS (rear-end collision avoidance system) has been developed as a system of ASV (advanced safety vehicle). It is a driver assist system to avoid the rear-end collision by informing the distance headway. It also has automatic braking function in case of emergency and distance warning function to the trailing vehicle. This paper describes the outline of RCAS, techniques about the preceding vehicle recognition and collision potential hazard evaluation. And experimental results about distance headway warning and collision avoidance by automatic braking are reported.