Showing papers on "Headway published in 1978"

A simulation study of alternative real-time bus headway control strategies

Abstract: Bunching of buses, due to variations in passenger loading, degrades service and operating efficiency. A simulation model is developed of a single-direction bus route, including explicit simulation of traffic signals. Using a hypothetical situation, several strategies are tested for the control of bus headways in real-time. These are: 1) holding points, 2) skippnig stops, 3) selective application of bus priority signalization, 4) reducing dispatch uncertainty. The last two prove most promising. It may be possible to field test selective application of bus priority signalization using existing computerized traffic signal systems. /Author/

Simulator for studying operational and power-supply conditions in rapid-transit railways

Abstract: The paper describes the development of a computer-based simulator which may be used to study the relationships between train movements and power-supply conditions in a 2-road rapid-transit railway. The work was specifically undertaken to enumerate the energy saving consequent on the introduction of chopper-controlled traction-control equipment with regenerative-braking capability. In the simulator, track topology and signalling constraints are represented by a sequential block structure which is analogous to the fixed-block signalling arrangements. Tractive characteristics of the traction equipment are represented by models which are train speed and line voltage dependent. Powering and braking trains are represented by piecewise linearised models and a complete power-network solution is obtained at each update period. The simulator is written in extended Fortran IV and is reasonably efficient in computer processing time; e.g. running a 1 h service at 90 s headway on a 5 km section of track typically requires 4 min of central processor time on an ICL 1906A. Simulating 20 km of double track, with up to 100 trains per track, typically requires 36 Kwds of core. Although the simulator was developed specifically for energy-consumption calculations, the methods of representation are quite general. The simulator may thus be used to study other problems of interest in train performance and signalling studies.

Modelling the Tendency of Buses to Form Pairs

Abstract: The paper describes a simple mathematical model of the behaviour of buses, on a relatively frequent service, after one has arrived at a stop at a time different from that scheduled. The model is similar to that used in some earlier papers on the pairing of buses, but derives a different objective function. Results are presented in terms of parameters relating to the scheduled headway h and the size of the initial deviation from it hd, the usual time spent by a bus at a stop, and the ratio k of the passenger arrival rate to the boarding rate. A graphical method was employed to find P, the number of the stop at which the first two buses form a pair. For the typical values of parameters used the relationship P = 1/6dk was deduced which, although no generality is claimed, can be used to set operational limits so that the bunching of buses does not occur. Limitations of the model are discussed.

Estimation of traffic platoon structure from headway statistics

Abstract: This paper deals first with the modeling of urban traffic headway statistics. It is shown that a composite distribution based on the convex combination of a lognormal and a shifted exponential distribution gives a good fit to observed traffic data. This statistical model is then used to generate a model for the formation and passage of "platoons" of vehicles. It is shown that the problem of estimating the time at which a "platoon" passes a detector, as well as the number of vehicles in the "platoon", corresponds to the point process disorder problem. An optimal estimator for the platoon size and passage time, based on detector data, is then derived via known results for the point process disorder problem. It is shown that the computations required by this estimator can be performed in a microprocessor. Furthermore, the estimator is tested-against the UTCS-1 traffic simulator and performs very well. Parameter sensitivity analysis of the estimator is presented. Finally, the use of these results to improve the filter/predictor described in a companion paper, and vice versa, is explained.

Optimizing urban mass transit systems: a general model

Abstract: This paper describes a model for determining the general dimensions of an optimal mass transit system for an idealized urban area. The model is based on a circular city with a definite center and with density declining uniformly form the center in all directions according to the negative exponential function. The transit system consists of radial routes that emanate from the center and contain descrete stops. Only trips to or from the center are considered, and travel is assumed to occur only in radial and circumferential directions. The model represents total community costs of the system, defined to include travel time, operating costs, equipment, and construction. A recursive procedure was devised to find a simultaneous minimum with respect to the spacing of routes, number and spacing of stops on each route, and average headway. Numerical analyses were conducted for six hypothetical cities by using varying values for the parameters of the density function. In each case, three types of transit systems were compared: conventional bus service, buses on exclusive lanes, and rail rapid transit. The optimal system in the largest city examined was exclusive bus lanes; in the other five cases, the optimal system was conventional bus service. Other interesting relations that appeared in the results are summarized. /Author/

The Effect of Small Cars on the Capacity of Signalized Urban Intersections

Abstract: Time headways between vehicles being discharged from a queue at a signalized urban intersection is a measure of the intersection's capacity. An event recorder actuated by tape switches on the road surface is used to measure headways at various signalized intersections in Toronto. The headways during saturation flow are related to the size of the vehicles and it is found that vehicles follow a small car with a closer headway than a full-sized car and a small car follows a vehicle closer than a full-sized car. The combined effect when both the lead and following vehicles are small cars is found to yield the smallest headways. This combined effect is most significant for the vehicles at the beginning of the queue. As a result, it is estimated that the capacity of a signalized intersection is increased by up to 15% for a stream of small cars over a stream of full-sized cars.

Swedish capacity manual. part 2. capacity of unsignalized intersections

Abstract: This paper presents a method for calculating capacity, queue length, and delay at unsignalized intersections that was developed for the recommended by the new Swedish capacity manual The method is based on a queuing model that considers each lane in the approaches controlled by yield or stop signs as a service position Service time is calculated, for each stream of vehicles in the lane, as a function of primary road flow rates and gap acceptance parameters The lane capacity is assumed to be the reciprocal of the mean of these service times Starting from the actual flow-to-capacity ratio, the queuing model estimates quenue length distribution and mean delay The method is believed to apply to most intersections controlled by yield or stop signs The most important parameters in the model is critical headway, which was measured at 18 Swedish intersections The results range between 33 and 75 s, depending primarily on direction, speed limit, and type of control; they generally agree well with those of previous studies A model similar to the one for unsignalized intersections was developed for traffic circles with short weaving sections /Author/

A State-Constrained Approach to Vehicle-Follower Control for Short Headway Automated Transit Systems

Abstract: Studies vehicle follower control in an automated transit system. In specific, presents a nonlinear feedback controller designed to operate at short time headways with kinematic constraint on vehicle operation.

The effect of presence lights on the detection of change of vehicle headway

Abstract: Previous experimental work has established a general relationship between light level and the detection of change in headway of a followed vehicle. It was assumed that the structure of the vehicle and its background had negligible effect on detection. Data are reported in the paper on the effect of simulating vehicle presence lights. The results suggest that presence lights make an insignificant difference to the detection of change of headway. This is further evidence that the original relationship can be applied in practical situations with confidence. Implications of the results to fixed and vehicle lighting design are discussed. Language: en

Technique for continuous recording of vehicle headway

Abstract: A technique for the continuous monitoring and recording of time headway, using an application of the coincidence method of measuring distance, was developed for application in a portable closed-circuit television system. The system provides in each recorded video frame the necessary information to determine distance of the lead vehicle and instantaneous time headway in any following episode. Provision is also made for recording vehicle braking and time cm task. The system has been used successfully over a period of 4 mo. incorporating 600 hr. of observation in over 14,000 miles of driving. It provides a continuous and unambiguous record of the driver's performance in relation to vehicles ahead in both day and night driving. It does not require the use of observers either on the road or in the driving cab and thus the setting for the driver is naturalistic. Finally, it is unobtrusive in the sense that the driver need never be aware of the component of his driving performance under study.

Programmable digital vehicle control system

Abstract: 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 7th 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 second) system.

Driver Performance and Fuel Economy

Abstract: Ninety drivers drove a city route under closely controlled conditions. Driver behaviors were scored and the vehicle was instrumented to record variables relevant to fuel economy. Fuel economy was related largely to average speed and number of variations in speed. Of the driver performance variables, only following distance related to fuel economy. Leaving adequate headway is a strategy that should result in both a saving in fuel and greater safety.

Edmonton's northeast light-rail rapid transit line

Abstract: Edmonton's light-rail transit (LRT) line has a total length of 7.2 km, 1.6 km of which is in subway. The line goes from the central business district (CBD) to the northeast sector of the city and uses the Canadian National Railways right-of-way. The project was approved at $65 million and is currently below estimates as well as ahead of schedule. The LRT line is the result of a balanced transportation plan that was finally adopted in 1974 to serve a city of nearly 500,000. The subway portion has two underground stations with full mezzanine floors. The mezzanine floors are part of an overall pedestrian system and connect with the basements of adjacent buildings. The subway was built to accommodate the largest standard subway car. The equipment specifications for the 14 articulated cars were based on performance and proven reliability. The construction methods used caused a minimum of interference in the CBD. Since relatively small portions were let successively, local contractors were able to use proven techniques to handle the work on a fixed-price basis. Despite the severe inflation of 1975 and 1976, costs were kept within reasonable limits. The proposed service will provide 5-min headways in the peak hour, giving a capacity of 5000 passengers/h. At midday the headway will be 10 min. The LRT line will be fully integrated with the bus transit system, and timed transfers will be provided between bus and rail. The LRT line in Edmonton makes use of available opportunities and provides the least expensive solution to the transportation problems of the northeast sector and its rapid residential development. /Authors/

Estimation of traffic variables using point processing techniques

Abstract: An alternative approach to estimating aggregate traffic variables on freeways--spatial mean velocity and density--is presented. Vehicle arrival times at a given location on a roadway, typically a presence detector, are regarded as a point or counting Poisson process whose rate is a function of the state of the traffic at every instant of time. Moreover, the traffic state is modeled as a finite-state Markov chain. A sequential point process filter, optimum in the mean-squared error sense, is designed to estimate the state from observations of the vehicle arrival-time sequence. Different possibilities for incorporating potential additional information such as speed and headway are explored. Parameter values for the underlying Markov chain are obtained via a maximum likelihood estimator. Qualitative behavior of the proposed algorithms is studied with simulated traffic flow data from both macroscopic and microscopic models.

A headway safety policy for automated highway operations

Abstract: The level of service, 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 (≥ 3,600 veh/lane/hr) over a range of typical highway speeds -- 13.5 -30 m/s (30.2 - 67.2 mph). 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 tradeoffs associated with safety, capacity and cost (in the form of required future development efforts.) are identified, and four parameter groups are selected as candidates for possible implementation.

The Application of Traffic Signal Preemption Systems for Controlling Bus Highways

Abstract: This report investigate the application of selective traffic signal preemption for controlling the headways of local service buses (buses with average time headways of less than 10 minutes), The preemption is selective in that it is granted to only "Iate" buses along a route, leading to a reduction. in headway variance. The potential benefits of more evenly spaced bus headways include reduced passenger waiting times, reduced incidence of bus overloadings and more efficient fleet operations. past applications of traffic signal preemption systems have concentrated on reducing travel times for buses in Central Business District (CBD) grids and arterials. However, these systems have not been widely accepted and implemented, indicating that the amount of reduction in travel time has not resulted in a sufficient increase in ridership to offset the systems costs and impacts on other traffic. The analysis and simulation results in this report indicated that selective traffic signal preemption is a feasible method for controlling the headways of buses on short headway routes. Furthermore, selective preemption yielded equal or better transit system performance compared to unconditional preemption with less than half as many preemptions and preempted cycle time. Future plans are discussed for expanding the simulation model developed in this report and continuing the analysis. The output of this work is expected to be a quantification of benefits as a function of bus priority variables, traffic variables and route characteristics.

A rail-transit people-mover headway comparison

Abstract: For many years, GRS has supplied control systems for conventional rail transit. Headways for these systems range from minutes or hours to as low as 75 seconds, In the last few years, the company has supplied control systems for people-mover applications in which minimum headways of 10 to 20 seconds have been achieved. The 75-second design headway of a model Conventional Rail Transit (CRT) system is compared with the 18-second design headway of a model Automated Guideway Transit (AGT) system from the viewpoint of potential for reduced CRT headway. It is shown that the major CRT factors responsible for this headway difference are on-line stations, train length and Safe Braking Distance. These factors are evaluated and discussed. It is concluded that a large increase in CRT track capacity should not be expected from the transfer of control technology from AGT.