Showing papers on "Traffic wave published in 1988"

Estimation of safety at signalized intersections (with discussion and closure)

Abstract: Models to estimate the safety of a signalized intersection on the basis of information about its traffic flow and accident history are provided They are based on data from 145 intersections in Metropolitan Toronto Several insights were obtained during the development of the models First, logically sound models require that the frequency of collisions be related to the traffic flows to which the colliding vehicles belong and not to the sum of the entering flows Second, it is therefore necessary to categorize collisions by the movement of the vehicles before the collision and not by the initial impact type, as is customary Third, the relationship between collision frequency and the related traffic flows is at times unexpected in form For each of the 15 accident patterns, an equation is given to estimate the expected number of accidents and the variance using the relevant traffic flows When data about past accidents are available, estimates based on traffic flow are revised with a simple equation Several practical questions can now be answered Given the traffic flow for a signalized intersection, one can predict how many and what kinds of accidents should be expected to occur on it; one can also show the probability density function (pdf) of the estimate Knowledge of the pdf allows the determination of what an unusually high number of accidents would be on such an intersection If the traffic flow of the intersection changes from year to year, one can estimate what changes in safety should be attributed to changes in flow Also, one can correctly compare the safety of several intersections that have different flow patterns Most important, one can estimate safety when both flows and accident history are given and, on this basis, judge whether an intersection is unusually hazardous This method of estimation is recommended for accident warrants in the Manual on Uniform Traffic Control Devices

Jams and superjams: a systems approach to congested traffic networks

Abstract: The road traffic engineer attempts to solve the problem of congestion and delay to road traffic in urban road networks by increasing capacity. He does this by computer control of traffic signals, by traffic management (one-way systems, banned turns etc.), by junction design, and to a limited extent by building new or improved roads. Such increases in capacity do not increase traffic speed if traffic demand is sufficiently high. However, they do increase the risk of traffic jams when blockages of the network, and especially of junctions occur, because there is increased traffic on essentially the same network as before. Traffic speed in congested road networks is set by an equilibrium with the best alternative public transport system. It can only be improved if public transport is improved and road space devoted to the more efficient user of space, the bus or tram, or, if demand is sufficiently high, by the construction of segregated rail systems.

Knosimo - a practicable simulation model for unsignalized intersections. intersections without traffic signals, proceedings of an international workshop, 16-18 march 1988, bochum, west germany

Abstract: This paper describes the knosimo simulation model, developed on behalf of the West German Ministry of Transport, which makes it possible to model the traffic flow at unsignalised intersections on a personal computer Its traffic flow simulation is based on a microscopic event-oriented approach; the elements of the model are the individual vehicles taking certain actions at certain events The vehicle headways in the model have a hyper-erlang distribution, to represent the occurrence of vehicle platoons, and the behaviour of individual vehicles is described in terms of their critical gaps and move-up times The knosimo program is written in pascal, and has different versions for different personal computer systems; its data is input through an interactive dialogue, directed by a menu of choices, where the user is asked to enter various characteristics of the traffic The results are presented as the means and standard deviations of various delay and congestion quantities for all traffic streams in all time intervals, together with various other statistics of these quantities The model can be applied to both urban and rural intersections with priority controlled according to specific West German road traffic regulations The results of the simulation usually agree well with those of corresponding theoretical and empirical studies As knosimo realistically describes the traffic conditions at unsignalised intersections, it can support the design of existing and new intersections, together with decisions about the necessity of traffic signals

A numerical methodology for analyzing traffic flow at congested surface streets

Abstract: A dynamic macroscopic methodology for analyzing traffic flow at congested intersections and arterial streets is presented in this paper. This includes complexities frequently encountered in practice such as turning and optional lanes, sinks and sources and spillback effects. The dynamics of interrupted flow under both sign and signal control are treated in an integrated fashion by considering the coupling effects of the main and side street flows. Compressibility is inherently included in the state equations employed; therefore dispersion and compression characteristics are built into the analysis. The proposed methodology is particularly applicable to severely congested networks at which spillbacks must be taken into account. Implementation of the state equations is performed numerically; this allows inclusion of stochastic and heuristic aspects for treatment phenomena that are difficult to deal with macroscopically. The modelling and numerical treatment employed is easily implementable to microcomputers (a).

Theory of highway traffic signals. final report

Abstract: This report gives a comprehensive survey of the theory of highway traffic signals including isolated signals, one-way arterials, two-way arterials, and networks, limited, however, to the common right angle junctions. The emphasis is on the logistics of control strategies rather than recipes for implementation. It is anticipated, however, that the implementation of some of the strategies described here will give substantial reductions in delays as compared with existing procedures.

The influence of partial constraint on delay at priority junctions. intersections without traffic signals, proceedings of an international workshop, 16-18 march 1988, bochum, west germany

Abstract: This paper presents a simulation model, in which delays at priority junctions can be determined under conditions of partially constrained, non-stationary traffic of varying intensity. Traffic is 'partially constrained' if not all drivers can maintain their desired speeds, due to the presence of other vehicles, and 'nonstationary' if its intensity varies with time. Within this context, any possible traffic streams at intersections of two two-lane roads can be considered. The method developed here will contribute to the decision whether to introduce traffic signals at an intersection. Simulation has been used to evaluate the influence of partial constraint on delay; some example simulation results are discussed in order to provide a first impression of the traffic intersection, for the example of a priority junction of two two-lane rural roads. The following conclusions are reached: (1) under partially constrained traffic conditions in the major road, the average delay decreases significantly in comparison to free-flow major stream traffic, whereas partial constraint on minor streams has insignificant effects on average delay; (2) a rapid increase in average delay compared to free-flow traffic occurs only under conditions of higher minor road traffic volume for partially constrained non-stationary traffic; (3) for constant total traffic volume on the major road, delay is reduced as the difference of directional traffic volumes decreases.

A numerical methodology for analyzing traffic flow at congested surface streets --14th arrb conference, 28 august - 2 september, 1988, canberra, act, australia; proc. parts 1 - 8

Abstract: A dynamic macroscopic methodology for analyzing traffic flow at congested intersections and arterial streets is presented in this paper. This includes complexities frequently encountered in practice such as turning and optional lanes, sinks and sources and spillback effects. The dynamics of interrupted flow under both sign and signal control are treated in an integrated fashion by considering the coupling effects of the main and side street flows. Compressibility is inherently included in the state equations employed; therefore dispersion and compression characteristics are built into the analysis. The proposed methodology is particularly applicable to severely congested networks at which spillbacks must be taken into account. Implementation of the state equations is performed numerically; this allows inclusion of stochastic and heuristic aspects for treatment phenomena that are difficult to deal with macroscopically. The modelling and numerical treatment employed is easily implementable to microcomputers (a). For the covering record of the conference, see IRRD no 808936.