Современные информационные технологии/Компьютерная  инженерия

Master student Ibrayeva N.N.,

students Amantaikyzy D., Baikara A.T., Mukhambetova M.A., Tuleubaeva F.M.

Research supervisor Candidate of Technical Sciences Kurmanov B.K.

Kazakh-British Technical University, Kazakhstan

Simulation Modeling of Urban Traffic with the Use of GPSS World

The rapid growth of the number of vehicles leads to an increase in traffic in the cities, the consequence of which is shown in the aggravation of traffic problems. Particularly acute they appear in the nodes of the road network – crossroads. There delays in traffic increase, long queues and huge traffic jams appear; it causes a useless fuel consumption, as well as increased wear of transport units and components. From an environmental perspective, the variable mode of movement, frequent stops and congestion of vehicles on the crossroads are the causes of high air pollution with the products of incomplete combustion in the city. An increase in the intensity of traffic and pedestrian flows also makes a negative impact on the road safety.

Today, there are over a dozen different models describing the traffic flow [1]. Simulation models solve the problem of constructing mathematical models that can adequately describe the behavior of the traffic flow and correctly reproduce the parameters and characteristics of the movement. The article shows the simulation model of the behavior of traffic flows on the crossroads using GPSS World simulation system [2]. The paper proposes a simulation model of the traffic on the city block, which is an intersection of several streets (see Figure 1). It is assumed that at each crossroad traffic lights are installed, in the figure these traffic lights are indicated by circles and numbered: 10, 20, 30 … . The traffic through the streets is two-way. In the figure the possible direction of vehicle is indicated by arrows and numbered. Turn left at the green traffic light is possible in the absence of oncoming traffic. Cars can drive into the block by 12 streets. In the figure, bold arrows indicate input streams of cars. The interval of cars coming is a random variable, subordinated exponentially. In the absence of interference the car passes the crossroad in a given time. There is given a probability of the car to go straight or to turn left or right on the crossroads.

Figure 1 – The scheme of traffic on the city block

It is assumed that all the cars on the block do not stop. In the absence of congestion, the car can pass the road from one node of intersection to another node for a random time, distributed under the normal law. In the case of severe congestion, there is given a number of cars that can accommodate from one intersection node to another intersection node. If the section of the street where the car wants to go or turn is filled, it can not pass through the traffic light, even if there is a green light. It is assumed that in the streets that go from blocks (in the figure they are shown by dashed arrows) there is no congestion, i.e. these streets cars can pass without delays.

There was developed a simulation program consisting of 20 segments, a fragment of which is shown in the Figure 2. 1 sec is adopted as a unit of time.

Figure 2 – A fragment of GPSS-program

In the first segment there is the original data set: the average interval of arrival of cars in a city block, the length of cars way through the intersection (with no interference), the rule of switching the traffic lights, the travel time from the intersection to the intersection (with no interference), the number of cars that can be on the road from intersection to intersection. Next nine segments simulate traffic flows at intersections. Another nine segments simulate the operation of traffic lights at intersections. In the 20^th segment the situation on the crossroads in every second is fixed (the state of queues, traffic condition, the presence of vehicle at the crossroads and on the streets, etc.) in order to animate the movement of cars on the city block. Finally, the 21th segment defines the end time of the simulation.

For observation of the simulation on the roads there was developed a program written on Java Script, allowing recreating the dynamics of the car movement by the results of historical data provided by the GPSS World system in a text file. Figure 3 shows a screenshot of the process of dynamic mapping of urban transport.

Figure 3 – Visualization of the simulation of urban traffic flow

On the developed model the length of the queue, forming at the traffic light under the different switching the traffic light laws (also when the switching time is determined by a function that depends on the length of the queue formed at a traffic light), was assessed.

Of course, by the increasing the size of the block under consideration the complexity of the model increases significantly. However, the use of GPSS World allows moving gradually from simple to more complex models step-by-step, so it reduces the overall complexity of the construction of complex models. The degree of the specification of simulation models of the processes is not limited, so it allows increasing the degree of their adequacy.

References:

1. Introduction to the mathematical modeling of traffic flows. Ed. A.V.Gasnikova. -M .: MIPT, 2010.

2. GPSS World Tutorial Manual. Copyright Minuteman Software. Holly Springs, NC, U.S.A. 2001.