Real time system example and algorithm

Introduction to Real time system: Real-time systems have been defined as: "those systems in which the correctness of the system depends not only on the logical result of the computation, but also on the time at which the results are produced". A real-time system is one that must process information and produce a response within a specified time; else risk apart the result, including failure. That is, in a system with a real-time constraint it is not having good chance to have the correct action or the correct answer after a certain deadline. Air line traffic control, automatic washing machines etc. are the examples of real time systems. It is of two types: Hard and Soft real time system.

    In hard real time system any output after the deadline should be treated as useless, so it lead to complete failure. For example, missile launching is the real time system. In a soft real-time system, degrading operations occur rarely and peak load can be tolerated. If load is high response time is reduced and hence minor delay can be there.

Now, as for as, the question is concerned, over here traffic lights are taken as real time system for description.

   Traffic lights: Traffic light is the hard real time system or intelligent system in which the time plays the major role. Time is set for the lights with the interaction of the physical world. The lights are used to reduce the delay while using the road by the vehicle.  The normal function of traffic lights requires sophisticated control and coordination to ensure that traffic moves as smoothly and safely as possible and that pedestrians are protected when they cross the roads. A variety of different control systems are used to accomplish this, ranging from simple clockwork techniques to sophisticated computerized control and coordination systems that self-adjust to minimize delay to people using the road.

   Traffic controller systems: A traffic signal is typically controlled by a controller inside a cabinet mounted on a concrete pad. Although some electro-mechanical controllers are still in use, modern traffic controllers are solid state. The cabinet typically contains a power panel, to distribute electrical power in the cabinet, a detector interface panel, to connect to loop detectors and other detectors, detector amplifiers, the controller itself, a conflict monitor unit, flash transfer relays, a police panel, to allow the police to disable the signal and other components.

                                        

                                              Computerized traffic control box

   Traffic controllers use the concept of phases, which are directions of movement grouped together. For instance, a simple intersection may have two phases: North/South, and East/West. A 4-way intersection has independent control for each direction. Traffic lights must be instructed when to change phase and they are usually coordinated so that the phase changes occur in some relationship to other nearby signals or to the press of a pedestrian button or to the action of a timer or a number of other inputs.

    The controller uses input from detectors, which are sensors that inform the controller processor whether vehicles or other road users are present, to adjust signal timing and phasing within the time limits set by the controller’s programming. Detectors can be grouped into three classes: in-pavement detectors, non-intrusive detectors, and detection for non-motorized road users.

   In-pavement detectors: These detectors are buried in or under the roadway. Inductive Detector loops are the most common type. They are sensors buried in the road to detect the presence of traffic waiting at the light, and thus can reduce the time when a green signal is given for an empty road. A timer is frequently used as a default during times of very low traffic density and as a backup in case the sensors fail. The sensor loops typically work in the same fashion as metal detectors.

   Non-intrusive detectors: It is sometimes more advantageous and cost effective to install over-roadway sensors than tampering the road and embedding inductive loops. These technologies include video image processors, sensors that use electromagnetic waves, or sound sensors to detect the presence of vehicles at the intersection waiting for the way.

   Non-motorized user detection: Non-motorized users are classified as pedestrians, bicyclists, and equestrians. Provisions for detecting these users include demand buttons and tuned detectors. Some traffic lights at pedestrian crossings, especially those away from junctions, include a button which must be pressed in order to activate the timing system. This is generally accompanied by a large display reading "wait", which lights up when the button is pressed, and off when the lights enter the red phase.

Now, describing the basic algorithm for the Traffic lights.  As the traffic lights are on the all four directions on the road. So the algorithm can be like as:

1.    Start

2.    Initializing and defining the variables and define the functions.

3.    Switch on Yellow on west direction and Red for remaining directions.  // west side is alert or ready and all other sides are restricted.

4.    Switch on Yellow on north direction and Red for remaining directions.

5.    Switch on Green on north direction and Red for remaining directions.

6.    Countdown timer is on, on the display.

7.    If Time is equal to zero.

      Goto step 8.

Else

     Wait for time to be zero.   //vehicle has to wait for the signal off

8.    Switch on Yellow on north direction and Red for remaining directions.   // north side is alert or ready

9.    Switch on Yellow on south direction and Red for remaining directions.

10. Switch on Green on south direction and Red for remaining directions. Goto step 6     // south side is free to move

11. Switch on Green on east direction and Red for remaining directions. Goto step 6

12.  Switch on Green on west direction and Red for remaining directions. Goto step 6

  This will keep on running at every time like this. Here is the flow chart representation of the traffic light algorithm.

                

   Traffic light are not only the alone part of the traffic control but there is the inter-relationship with the other phases, which gives the better understanding of the traffic control system. It is shown in the diagram below.

Traffic light control and information transmission device compromising a microprocessor on the cross road, the microprocessor further connects to a traffic light controller, an electronic display board, a video camera, a compression circuitry, an I/O interface, a traffic flow detector and connected to the central traffic control computer through the DSL (Digital Subscriber Loop). The control signals, traffic, public information or news of the central traffic control computer can go through the DLS to the microprocessor; the microprocessor can control the traffic light and display all the information on the electronic display board. The traffic flow data of the cross roads can be accessed by the traffic flow detector and the video camera and transmitted back to the central traffic control computer.

   Suggestion for required modification: The future traffic lights should be more interactive. As in the present traffic lights the countdown timer displays the numbers which are not mostly liked and may annoy someone waiting in red signal. Interaction can be done like as when signal becomes red the days headline news can be displayed or weather can be displayed simultaneously with the interactive countdown of traffic light device.