حركة السير في المدينة - تنظيم حركة السير .. الحاسبات تعمل

Traffic in the city - Traffic regulation .. Computers work

Traffic in cities is usually regulated either by traffic lights at intersections or by a traffic policeman. The traffic policeman is more effective than regular traffic lights as he can regulate traffic according to its density in different directions and at adjacent intersections, which of course traffic lights that change automatically every specific period of time are unable to do.

However, the control of the electronic computer over traffic lights at a group of adjacent intersections is close in flexibility to its regulation of traffic

(The soft pedals on the road send signals to the central computer, which controls the traffic lights using a timing mechanism. Workers in the main control center monitor traffic using television cameras).

(A computer-controlled traffic light control system (top figure) Television signals (1), monitor (B), circuit breaker box (C), monitoring printer (D), traffic detector (E), control and signal discharging computers (F). Main control center (bottom figure).

A traffic policeman is assigned to each intersection, and in addition to that, he is able to coordinate traffic in an entire area, as he adjusts the traffic lights at all intersections to ensure the best traffic movement in all directions.

The computer takes into consideration and continuously changes the traffic movement everywhere, and in emergency situations organizes the passage of ambulances, fire trucks and police as quickly as possible, choosing the shortest and least crowded paths to the intended location, and lights the green light along the selected roads.

This system consists of a central computer with information about the flow of traffic through special traffic detectors placed in many places in the concerned area. The computer sends electrical signals to control all traffic lights in the area according to the current traffic conditions and certain traffic control rules included in the computer program. The system's operating principle is simple in principle despite the complexities caused by the abundant stream of signals coming from traffic detectors and going to traffic lights, as the system may include hundreds of traffic lights and regulate the traffic of thousands of cars in the concerned area.

The devices installed on the roads are divided into three categories, according to the functions they perform, which are: detecting the presence of vehicles, controlling the flow of traffic, and monitoring the traffic condition to ensure the performance of the entire system. These functions are usually performed by separate equipment, and the devices that monitor traffic are not connected to the central computer.

The presence of vehicles is detected by means that are separated on the road at intersections and in other suitable places, and generate an electrical signal whenever a vehicle passes over it. These media are usually of two types, either soft treadmills, the air pressure inside of which increases whenever a vehicle passes over it, which activates an electric circuit breaker that works by air pressure, or they are of the type that works by magnetic induction, generating electrical signals when "metallic objects" approach. The signals resulting from these detectors are sent to the main control center via electric cables, and one cable may carry signals from several detectors.

The traffic lights control the flow of traffic, and the circuit breakers with a timing mechanism are turned on and off from its box, and the electronic computer adjusts the length of their time cycles. The box always shows the status of the traffic lights in the main control center.

Traffic is monitored by television cameras installed in suitable places and their images are transmitted in a closed circuit to display screens in the main control center. Human observers can change the direction of these cameras.

(Part of the one-way traffic control system, and the locations of the devices on the streets are shown in the upper section)

(Context diagram for the signal disposal computer).

And adjust their focus Remotely, to allow them a clearer vision, especially in emergency situations and traffic obstruction. This monitoring system is not linked to the computer and may be dispensed with in some cases.

The main control center is equipped with two electronic computers and a display panel that shows the density of traffic and the status of traffic lights in the area, and television surveillance screens. Each of the computers usually has a backup computer that replaces it if it breaks down or during routine maintenance. System supervisors can bypass the computer in emergency situations or complete breakdowns, and they can contact the police or other official bodies by phone or wirelessly.

A computer is allocated for control and another for disposing of the large number of signals that reach and are issued by the center. If the system includes a thousand traffic detectors, each detector emits an electrical signal when a vehicle passes over it, and if a thousand cars pass over each detector per hour, the signals are returned to the center at a rate of approximately three hundred signals per second. If the control computer takes over these signals and those sent to the traffic lights, it will not have enough time to perform its task at the required speed.

Each blocked traffic detector is allocated a storage space in the signal processing computer where the information received by the control center is stored. The computer's processor examines each blocked detector in turn at a rate of approximately one hundred times per second. If there is a change in the stored number due to signals received from the relevant detector since the last inspection, the control computer is informed of this in order to update the traffic status record stored in it. The signal processing computer is also responsible for sending signals to the timing mechanisms in the switchboards.

Whenever a signal is received from a box indicating a change in the traffic light, the signal processing computer responds by determining the next timing cycle.

The control computer keeps in its main notebook a record of the traffic density in each section of the area's roads, the current status, and the timing of each group of traffic lights. This information is shown to the observers on a display map.

The computer also stores the control program that directs the computer to examine the traffic flow towards each intersection in turn, to determine the number of vehicles coming from each direction, and to use this information in calculating the ratio of the green light period to the red light period for each intersection. The control program takes into account the congestion conditions on the desired roads and adjusts the timing of the lights to facilitate the flow of traffic as much as possible.