Showing papers on "Headway published in 2000"

Headway on urban streets: observational data and an intervention to decrease tailgating

Abstract: A method to collect headway (tailgating) data in an urban setting was implemented and produced reliable headway data on over 25 000 drivers. Data are reported on the effectiveness of two hand-held roadside signs admonishing drivers not to tailgate. One of these signs (that included a reference to “crashes”) had a significantly positive impact on drivers' headway. Drivers’ followed with an average headway of 2.11 s when the sign was absent compared to an average headway of 2.29 s when the sign was present. When the sign was absent, 49.4% of the drivers were in compliance with the 2-second rule compared to 57.5% when the sign was present. The percentage of drivers who followed with a headway of less than 1 s decreased from 7.3 when the sign was absent to 3.0 when the sign was present. Additionally, there was an increase of 10.6 ft in vehicle separation from baseline to intervention.

Continuum approach to car-following models

Abstract: A continuum version of the car-following Bando model is developed using a series expansion of the headway in terms of the density This continuum model obeys the same stability criterion as its discrete counterpart To compare both models we show that traveling wave solutions of the Bando model are very similar to those of the continuum model in the limit of small changes of headway As the change of headway across the wave increases the solutions gradually diverge Our transformation relating headway to density enables predictions of the global impact and characteristics of any car-following model using the analogous continuum model In contrast, we show that the conventional continuum models which account for effects of pressure and dispersion predict behavior which is distinct from the global behavior of discrete models

Effects of variable message signs for slippery road conditions on driving speed and headways

Abstract: This field study investigated the effects of two variable message signs (VMS) on driver behaviour. Specifically, the signs were a warning sign for slippery road conditions and a minimum headway sign. The study was performed as a before-and-after experiment at three test sites in Finland with an after period covering two winter seasons. The results showed that the slippery road condition sign reduced the mean speed on slippery roads by 1–2 km/h in addition to the decrease caused by the adverse road conditions. The minimum headway sign decreased the proportion of headways shorter than 1.5 s for cars in car-following situations, in addition to a speed reduction of 1 km/h. The effects were somewhat smaller during the second winter than the first.

The BMW Active Cruise Control ACC

Abstract: This paper describes the BMW Active Cruise Control (ACC) system which adds a headway control function to the speed control function of conventional cruise control systems. The functions of the ACC are described, including the system capabilities, limits, function design and system philosophy. This is followed by a description of the system, its components, and its control functions. The paper concludes with a discussion regarding the safety concepts of the combined sensor control unit and of the entire system network.

Optimal feeder bus routes on irregular street networks

Abstract: The methodology presented here seeks to optimize bus routes feeding a major intermodal transit transfer station while considering intersection delays and realistic street networks. A model is developed for finding the optimal bus route location and its operating headway in a heterogeneous service area. The criterion for optimality is the minimum total cost, including supplier and user costs. Irregular and discrete demand distributions, which realistically represent geographic variations in demand, are considered in the proposed model. The optimal headway is derived analytically for an irregularly shaped service area without demand elasticity, with non-uniformly distributed demand density, and with a many-to-one travel pattern. Computer programs are designed to analyze numerical examples, which show that the combinatory type routing problem can be globally optimized. The improved computational efficiency of the near-optimal algorithm is demonstrated through numerical comparisons to an optimal solution obtained by the exhaustive search (ES) algorithm. The CPU time spent by each algorithm is also compared to demonstrate that the near-optimal algorithm converges to an acceptable solution significantly faster than the ES algorithm.

Delay-based passenger car equivalents for trucks at signalized intersections

Abstract: This paper presents a new methodology for computing passenger car equivalents at signalized intersections that is based on the delay concept. Unlike the commonly used headway-based methods that consider only the excess headway consumed by trucks, the delay-based approach fully considers the additional delay heavy vehicles cause on traffic stream. Delay-based passenger car equivalents are not constant, but depend on traffic volume, truck type and truck percentage. The field data indicated that the passenger car equivalents increase as the traffic volume and the percentage of heavy vehicles increase. The field data were used to calibrate TRAF-NETSIM simulation model that was used to cover a broad range of traffic conditions. Mathematical models to estimate the equivalencies were developed. The passenger car equivalent for single unit trucks vary from 1.00 to 1.37, and for combination trucks 1.00–2.18 depending on traffic volume and truck percentage. The passenger car equivalents are highly correlated with traffic volume and, to some degree, with percentage of heavy vehicles. Although the PCE of 1.5 recommended in the 1985 HCM seems to be more reasonable than the 2.0 recommended in the 1994 and 1997 HCM, both overestimate the impact of single unit trucks. For combination trucks, the 1997 HCM overestimates the capacity reduction effects of the trucks in most cases.

Effects of variable message signs for slippery road conditions on reported driver behaviour

Abstract: A field study by Rama and Kulmala (Rama, P., Kulmala, R. (2000). Effects of variable message signs for slippery road conditions on driving speed and headways. Transportation Research, Part F, 3, 85–94.) showed that a variable message sign warning about slippery road conditions reduced the mean speed by 1–2 km/h. The study also showed that a variable message sign recommending a minimum headway between vehicles decreased the proportion of short headways. However, the signs may have other effects on driver behaviour besides those measurable in terms of speed and headway, and this study was designed to investigate such potential effects. In total, 114 drivers who had encountered the slippery road condition sign and 111 drivers who had encountered the sign showing recommended minimum headway in adverse road surface conditions were interviewed. The results suggested that these variable message signs do indeed have other effects, such as the refocusing of attention to seek cues on potential hazards, testing the slipperiness of the road, and more careful passing behaviour. On the other hand, the results suggested that driving speed and headway are essential variables with which many other variables correlate.

Traffic Management Parameters from Single Inductive Loop Detectors

Abstract: Investigated are potential new uses for the digital output produced by single inductive loop detectors (2 m x 1.5 m and 2 m x 6.5 m) used in most European urban traffic control systems. Over a fixed time period, the average loop-occupancy time per vehicle (ALOTPV) for a detector being sampled every 250 ms is determined by taking the number of 250-ms occupancies and dividing by the number of vehicles. In a similar way, the average headway time between vehicles (AHTBV) is determined by taking the number of 250-ms vacancies and dividing by the number of vehicles. Over a 30-s period, the minimum and maximum values of ALOTPV and AHTBV ranged from 1 to 120 (an ALOTPV of 1 and an AHTBV of 120 representing free-flow conditions, an ALOTPV of 120 and an AHTBV of 1 representing a stationary queue). Identifying periods when a link was operating under capacity and at capacity and when it had become saturated could be more clearly identified by using plots of ALOTPV and AHTBV data over time compared to the more traditional percentage occupancy output. ALOTPV also was used to successfully identify long vehicles from cars down to speeds of 15 km/h.

Development of an adaptive cruise control system with brake actuation

Abstract: An adaptive cruise control (ACC) system has been developed by using an electronically controlled vacuum booster for smooth brake control and millimeter-wave radar that operates effectively even in rainy weather. The headway control unit was designed based on an analysis of driving behavior characteristics and achieves natural vehicle behavior that does not seem strange to drivers. This paper presents an outline of the system along with the results of simulations and driving tests. The effectiveness of the system was evaluated with a driving simulator and in vehicle tests, and the results verified that it reduces the driver's workload. (A) For the covering abstract see ITRD E106371.

Enhancements of CORSIM Model in Simulating Transit Operations

Abstract: A CORSIM-based microscopic simulation model is developed, which provides transit planners and operators with the ability to simulate bus operations on transit routes. Several modules in CORSIM for processing bus operations are modified to calculate bus dwell times at stops. The bus dwell time is dynamically determined by the passenger arrival rate, average boarding time, and vehicle interdeparture time (headway). Bunching of buses—due to variations in passenger demand at stops, travel times on streets, and delays at intersections—deteriorates the quality of service and operating efficiency, which can be observed from the simulation results. The input requirements and the modular nature of the proposed model are highlighted. Outputs, including bus arrival and departure times, dwell time, and average passenger waiting time at each stop, are generated for the evaluation of bus operations. The proposed simulation model is calibrated and validated by two sets of data collected from bus route 39 of the New Jersey Transit Corporation.

A multisensor-based collision avoidance system with application to a military HMMWV

Abstract: A multi-sensor collision avoidance system (GAS) presented in this paper is based on a fusion scheme that utilizes fuzzy clustering and estimation techniques. Measurements from radar, vision and sonar are discriminated, fused and used to estimate relative motion between the prime and front vehicles. The estimated motion is then used to predict possibility of collision with the vehicle in the headway. Fuzzy logic is employed to initiate an audio and visual warning system. It also deploys a throttle relaxer and brake actuator to slow down the prime vehicle. Simulation study was carried out to evaluate the CAS concept. An actual concept prototype was implemented on a military vehicle to validate the feasibility.

Fleet study evaluation of an advance brake warning system.

Abstract: The advance brake warning system (ABWS) is a mechanism that activates the brake lights in response to a rapid disengagement of the gas pedal, before the driver's foot reaches the brake pedal. Two previous studies showed that (a) such rapid releases of the gas pedal are typically followed by brake activation, and (b) the ABWS can prevent a high percentage of rear-end collisions in which an attentive following driver maintains a headway of 1.0 s or less from the vehicle ahead. In the present study the crash involvement of 764 government cars and light trucks was tracked over an average period of 35 months. The vehicles were matched in pairs--one of each pair with the ABWS and one without it. Data analyses focused on collisions in which the government vehicles were rear-ended. Overall, ABWS-equipped vehicles were not significantly less involved in rear-end collisions. However, an examination of the struck vehicles only showed that the ABWS-equipped vehicles were involved in fewer rear-end collisions per kilometer driven than were the vehicles without the ABWS. In conclusion, despite the theoretical appeal and the results of earlier studies, the fleet study failed to demonstrate that such a system is a cost-effective safety device for the prevention of rear-end crashes. Actual or potential applications include the evaluation of new in-vehicle technologies by a hierarchy of multiple validation studies prior to consideration.

Findings on the Approach Process Between Vehicles: Implications for Collision Warning

Abstract: Over the past 10 years there has been a growing body of research into modeling and describing driving behavior, particularly for situations that occur on motorways. This interest has arisen from the need to assess safety and capacity benefits that could be produced by changes to road design, operation, signage, and in-vehicle advanced transport telematics, such as collision warning (CW) or autonomous cruise control. For the most part these investigations have focused on "close" or "car" following, which describes the maintenance of a time- or distance-based following headway. However, often overlooked, and of equal importance, is the "approach" process, describing how a driver decelerates when approaching a slower vehicle. There are several competing theories of the behavioral basis underlying this process, including, for example, those based on time-to-collision or optic flow. There are, however, very few data against which such models can be assessed and systems designed. Presented are the results from ...

Development of capacity estimation method from statistical distribution of observed traffic flow

Abstract: The objective of this study is to present a quantitative method for highway capacity determination by evaluating alternative approaches in developing capacity from the statistical distribution of observed traffic flow. Extremely long headways are considered to be unreasonable for sufficient demand and for the maximum flow rate defining capacity. Therefore, the longer headways are removed from measured data. To determine the threshold which defines "long headways" confidence intervals of 90%, 95%, and 99% from headway distribution have been used. Further, cumulative distribution of volumes were evaluated at their 85, 90, and 95 percentiles. Then the composite evaluation of headways corrected by the "long headway" and volume distribution percentiles is performed. The result revealed that maximum flow rate is between 2,130 pcphpl (passenger cars per hour per lane) and 2,315 pcphpl. Compared to the capacity of 2,200 pcphpl used in the Korea highway capacity manual, capacity appears to correspond to a confidence headway interval of 95%. The study suggests that the rational capacity estimation alternative is to take the 95% of cumulative distribution of observed traffic flows at 95% confidence headway interval eliminating 5% of long headways (i.e., 95-95 Rule).

Headway-based bus priority in London using AVL: first results

Abstract: Bus priority is being widely implemented across many UTC areas in London, following successful field trials in the EC-funded projects PROMPT and INCOME. Installation has now been completed at over 100 junctions, with full evaluations being undertaken in each case. The remaining roll-out programme includes over 500 additional junctions. This roll-out has initially been based on the existing technology of bus transponders and inductive loop technology. However, the committed London-wide implementation of automatic vehicle location (AVL) technology for fleet management and passenger information at bus stops offers the potential to use new technology and more sophisticated control for bus priority. In particular, the real-time bus location information, provided by AVL, enables the level of priority provided for each bus to be tailored to its needs. The possibility of using AVL to support bus priority at traffic signals in London was raised in the early 1990s, when the first AVL-based COUNTDOWN trials were commissioned. A feasibility study undertaken for London Transport Buses (LTB) by the Transportation Research Group (TRG) at Southampton University indicated potential benefits and likely cost-effectiveness. A method of selective priority for buses, that differentiates between buses based on their headways, was developed and evaluated by TRG using simulation. This method was integrated into the bus priority system, and known as the Headway Regularity Algorithm. System commissioning on a section of the Uxbridge Road was undertaken in 1998/99, leading to technical trials and the first live trials in June/July 1999. The paper summarises this research, development and installation process before describing the first results of the trials in more detail.

Impedance control for truck collision avoidance

Abstract: We describe the results from a series of experiments using the "virtual bumper" collision avoidance algorithm implemented on a Navistar International tractor cab. The virtual bumper combines longitudinal and lateral collision avoidance capabilities to control a vehicle in both normal and emergency situations. The motion of the vehicle is modified based on sensed incursions into a programmable "personal space" around the vehicle. An impedance controller determines the dynamics of the vehicle response. Radar integrated with a laser range finder are used to sense vehicles in the forward field of view of the host vehicle. The results of two driving scenarios are presented. The first scenario tests the system's ability to stop the tractor at a safe headway in response to a stationary vehicle. The second scenario demonstrates the adaptive cruise control (ACC) functionality implemented using the virtual bumper. In this scenario, the test vehicle is able to safely stop when the preceding target vehicle suddenly decelerates to a stop. The system has been successfully tested in a variety of other situations as well. The virtual bumper proved effective in ACC scenarios, major traffic slow down situations, sudden target acceleration/deceleration and in stop and go traffic.

Modeling vehicle headways for low traffic flows on urban freeways and arterial roadways

Abstract: One of the important microscopic flow characteristics that affects safety, level of service, driver behavior, and capacity of the roadway is vehicle headway. The time between arrivals of successive vehicles passing a point on roadway is called vehicle headway. This study aims at analyzing the vehicle headway for urban freeway and arterial roadway sections in Riyadh (capital of Saudi Arabia) and comparing them with results from international research. Only low volume traffic conditions is of the concern in this research. The paper describes the mathematical distribution for vehicle headway data on two types of roadways (freeways and arterials). The study found that shifted exponential distribution and gamma distribution appear to reasonably fit data from freeways and atrerials, respectively.

Development of Daihatsu ASV2

Abstract: We are developing the ASV2 experimental vehicle. We report on the lane keeping system and the driver model. The lane keeping system is a steering control system without driver operation. We report an algorithm that adapts sliding mode control to lateral control and gets the most suitable angle. Our driver model is able to calculate critical distance headway for individual drivers by learning the driver's driving characteristics and is able to warn of a collision hazard. The effectiveness of this model is shown by the results of an experiment.

Simulated Relationships between Highway Capacity, Transit Ridership, and Service Frequency

Abstract: This article analyzes the relationships between highway capacity additions and transit patronage, both in the short and long run. A methodology using a model of schedule disutility is shown to provide a technique to account for transit service frequency. This technique, combined with a supply-side model of a highway corridor is used to evaluate the impact of transit headway changes and highway capacity, increases in total transit ridership, using a synthetic sample of commuters. Simulation results are used to evaluate the impact on travel times and utility of the two modes and the long-run degredation of transit service predicted by the Downs-Thomson paradox. While the results do not show congestion as necessarily being worse than before capacity expansion, they do show that transit service frequency could be reduced significantly over time.

Object recognition algorithm for adaptive cruise control of vehicles using laser scanning sensor

Abstract: Not merely running at the designated constant speed as the classical cruise control, the adaptive cruise control (ACC) maintains safe headway distance when the front is blocked by other vehicles. One of the most essential part of ACC system is the range sensor which can measure the position and speed of all objects in front continuously, ignore all irrelevant objects, distinguish vehicles in different lanes and lock on to the closest vehicle in the same lane. In this paper, the hierarchical object recognition algorithm (HORA) is proposed to process raw scanning laser data and acquire valid distance to target vehicle. HORA contains two principal concepts. First, the concept of life quantifies the reliability of range data to filter off the spurious detection and preserve the missing target position. Second, the concept of conformation checks the mobility of each obstacle and tracks the position shift. The algorithm is emulated on computer and tested on line with our ACC vehicle.

AFTS-Automated Flexible Transportation System: a new concept for urban mass transportation

Abstract: This paper deals with the concept of an automated flexible transportation system (AFTS) for urban mass transportation composed of transit 'bus or van platoons that, using dedicated lanes in public avenues common in large metropolitan areas, may improve positively the urban transportation network, increasing passenger capacity and reducing the vehicles' headway when compared with conventional systems. To achieve this purpose, an automatic guidance control housed inside the vehicles, in the absence of any driver's interference in the automated lane sections, will be interacting with a wide range of vehicle and ground lane sensors, communicating with the dedicated central system computer cluster, being able to increase significantly the overall average speed and reduce dramatically the distance between vehicles in the platoon formation, having pre-programmed stop stations located on central aisles. A feasibility study of the conceptual system was performed assessing the cost-benefit ratio of the proposed system. Finally, the paper shows some simulation results using preliminary adaptive controller scheme, simplified platoon dynamic model and the available field data information to evaluate overall system.

The prediction of transit arrival times using link-based and stop-based artificial neural networks

Abstract: Transit operations are disturbed frequently by stochastic traffic variations and ridership, which may deteriorate schedule/headway adherence and thus lengthen passenger wait times. Providing accurate and accessible information on transit vehicle arrival times is critical to improve transit service quality. In this study, both link-based and stop-based artificial neural networks (ANNs) are developed for predicting bus arrival times in real time. The accuracy of the ANNs are assessed through simulating NJ Transit Route #39 and conducting reliability analysis for predicted bus arrival times. The results show that the link-based ANN performs well at stops with fewer intersections in between, while stop-based ANN can adapt to variation in traffic conditions between stops with more intersections. The study provides an efficient computer program that can be used to integrate and evaluate innovative models and strategies for promoting service quality.

On-Road Investigation of Driver Following and Deceleration on Surface Streets

Abstract: This paper describes a study in which male and female participants in three age groups drove an instrumented vehicle on a 20mile (32.2km) route while information about their driving and following behavior was recorded. The drive included frequent following and stopping. Dependent measures of interest included following headway, range and range-rate, deceleration levels, and braking behavior. Following below a 1.0s headway occurred infrequently. Two modes of manual deceleration control based on initial inter-vehicle conditions prior to deceleration and brake covering behaviors are described.

New Headway English Course, Elementary, Student's Book

Abstract: New Headway English course: elementary: student's book , New Headway English course: elementary: student's book , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Electronic tailgating deterrents: the 'two second gap' project

Abstract: Vehicle tailgating is one of the most significant causes of rear end collisions. The goal of the 'Two Second Gap' project is to develop electronic devices that can be used to discourage tailgating. This paper presents the developmental progress on two devices which have been researched to date. A roadside monitoring system has been designed which detects when passing vehicles are tailgating. This enables offenders to be warned or fined and can collect vehicle headway statistics. These statistics may be used in identifying trouble spots or evaluating the effectiveness of deterrent programs. Preliminary trials of the monitor have shown that at times nearly 20 percent of Brisbane drivers are following twice as close as the recommended safe following distance. The project's main focus has been in designing an in-vehicle, low-cost sensor that warns the driver if they are tailgating, or if there is a collision imminent. Ideally this system will help to modify driver behaviour to avoid tailgating. Both of these devices have been successfully developed and are waiting to be adopted by authorities and manufacturers. (a) For the covering entry of this conference, please see ITRD abstract no. E202376.

Comparing Performances of Turbo-roundabouts and Double-lane Roundabouts

Abstract: Starting from assumptions regarding the arrival process of circulating streams and according to models based on the gap-acceptance theory, the paper is aimed at comparing operational performances between basic turbo-roundabouts and double-lane roundabouts. The paper proposes applications of the Hagring model for entry capacity estimations at double-lane roundabouts and turbo-roundabouts, these latter, in particular, featured by movements with only one or two conflicting traffic streams. This model allows to use, in fact, a bunched exponential distribution to quantify the distribution of major vehicle headways; it also considers specific values different by each lane for behavioural parameters, minimum headway and conflicting traffic flow on circulating lanes. The results obtained for the two cases examined, although influenced by the underlying assumptions, especially with regard to user behaviour at turbo-roundabouts, can give information about the convenience in choosing, at a design level, a basic turbo-roundabout rather than a double-lane roundabout. The comparison developed in this paper, indeed, can be helpful in selecting the type of roundabout and in particular in evaluating performance benefits that are obtainable from the conversion of an existing double-lane roundabout to a turbo-roundabout with similar footprint of space.

Method of Designing Acceleration Lane Length in Freeway Interchange

Abstract: The length of an acceleration lane in freeway merging area is investigated with probability theory in this paperAn algorithm for designing the length of acceleration lane is shownIt provides theoretic foundation for designing the optimal length of acceleration lane in our country