Showing papers on "Traffic wave published in 1979"

A Two-Fluid Approach to Town Traffic

Abstract: A two-fluid model of town traffic has been developed by extending ideas formulated in an earlier kinetic theory of multilane traffic. The-two fluids are taken to consist of moving cars and cars stopped as a result of traffic conditions. The average speed of the moving vehicles is assumed to be proportional to the fraction of the vehicles that are moving raised to a power that reflects the "goodness" of the traffic. It is then found that the trip time per unit distance is essentially linearly related to the stop time per unit distance, in general accord with data obtained in many cities. Relations are developed on this basis for flow, among other variables, versus average speed. These relations contain a new parameter that is identified with the quality of the traffic network system.

Estimating the time costs of highway congestion

Abstract: Previous estimates of the magnitude of highway congestion costs have employed equations relating the external cost imposed on motorists by an additional vehicle to the speed of traffic flow or the ratio of traffic flow to the maximum capacity of the road. While those equations may be accurate for rural roads and expressways, they may be less accurate on city streets where delays at intersections are a dominant factor in congestion costs. This study replaces single speed-volume equations with a traffic simulation model that replicates the queuing of vehicles at traffic lights, the dispersion of platoons of vehicles as they move from one intersection to another, and the interaction of intersecting traffic flows on an urban street network. The model is used with actual Toronto road and traffic data to produce new estimates of congestion costs on specific streets during the morning rush hour. The model produces a surprisingly high average congestion cost during the morning rush hour and a poor correlation of the results with those that would be estimated for the same traffic flows by the single equation models. The simulation technique allows the calculation of congestion costs on a street-by-street basis, generating the detailed information that would be necessary for a complex congestion pricing scheme. TRAFFIC CONGESTION IN URBAN AREAS has long been recognized as a technological external diseconomy causing serious urban problems. Highway engineering studies show that over a range of traffic flow levels observed on city streets an increase in the volume of traffic flow will reduce the speed of that flow for all motorists. While the additional driver perceives the impact of this lower speed upon himself, he is not faced with the social costs of the time lost to all other motorists as a result of his entering the road. The private cost of using the road, as perceived by the added motorist is thus below the social cost, often by a large amount. It has been shown that if the marginal external social cost of an additional vehicle-mile can be calculated and a toll is charged to all motorists equal to this marginal external cost, a Pareto improvement in the efficiency of using the road can be achieved.2 Mohring [10] has estimated the magnitude of such tolls as a function of the volume/capacity ratio of the highway, a measure of capacity utilization. Johnson [6] calculated a similar set of tolls as a function of the speed of movement of traffic on the road. Walters [15] estimated the elasticity of costs with respect to speed or time of travel. Smeed [13] calculated congestion costs as a function of speed and of the volume/capacity ratio.

Traffic demand estimation model by observed arc flows regarding generation trips as unknowns

Abstract: In the suggested model the demands for all kinds of traffic in the road network can be estimated by finding in every node only the volume of generated traffic corresponding to the observed volume of traffic in the road section, because the difference between the volumes of generated and concentrated traffic in a network node is equal to the difference between total traffic outflow and inflow in road sections adjoining to the node. Flow chart of evaluation method is given and estimation accuracy for different kinds of traffic demands is discussed.

The traffic flow theory

Abstract: The basic parameters of the time and space distributions of road traffic are defined in this paper and their inter-relationships derived. Inclusion of slowness, the reciprocal of speed, enables the author to show that each parameter of one distribution has a corresponding parameter in the other, and that relationships exist between the space and time slowness parameters which are of the same form as those involving speed. (TRRL)

Delays at priority intersections under non-stationary traffic flow conditions

Abstract: The history of the derivation of capacity calculations under steady state conditions is outlined by the authors who use a model based on the Monte Carlo method to consider non-stationary flows. An approach is used in which the traffic intensity follows a rectangular form in time remaining constant for one minute. Simulated delays under non-stationary conditions are shown to be nearly four times longer than those predicted for stationary conditions, although the number of vehicles on both major and minor roads remained unaltered. The greatest delays occurred some minutes after the period of greatest flow depending on the demand/capacity profile. A family of delay curves has been obtained from several hundred one-hour simulations. The variation of capacity as a function of the major-road traffic flow is investigated. Measurement of actual delay times confirm those predicted by theory. (TRRL)