Control System: Traffic Light Control System

Initial Idea:
  • As a kid, I thought that there was some studio in the city, were numerous people sat and monitored traffic on a monitor. They would then hit different switches to determine which stop would get a green light.
  • Later, after my grandfather explained to me that sensors in the ground (either responding to weight or an inference in the magnetic field) indicate that there is a queue of cars weighting for the light to turn green, thus the specific traffic light is queued up for turning green next.
  • I also think that the opposite light to the traffic light you are at also goes green, however, not if it is a light indicating that you can make a turn to the left/right.

  • After some computer science classes, I predict that all the traffic lights are entered into a program. Through CCVT and sensors in the ground, it is detected whether to queue up the specific traffic light or not. Logic gates (learned this concept in CS classes) should be used to determine, which lights need to go off when others are turned on. The switching between lights should be alternating. Furthermore, CCVT are needed for predicting traffic jams and timing how long the light must be switched from red to green.


Purpose of a control system:
  • To measure, monitor & control a process
  • Feedback signal
    • Measuring of output

  • Open-loop
    • Open-ended, no feedback system
    • Output has no effect on control of the action à manual operator
      • Output not measured/monitored
      • Few automatic/feedback features
      • Characteristics:
i. Actual and desired output not compared
ii. No regulation of output value
  • Closed-loop (also known as feedback control system)
    • Uses concept of open-loop, but includes one or more feedback loop (paths between output & input)
      • Portion of output returned back to input to check whether it is desired value and reduce error
        • Returned until error reduced à control adjusted
        • Designed to achieve/maintain desired output
      • Uses feedback signals
      • Characteristics:
i. Reduce error by adjusting input (feedback = new input)
ii. Improve stability of unstable system
iii. Increase/reduce system sensitivity
iv. Reduce reliable performance

Traffic Light Specific Background Information
  • Phases
    • o Grouped directions of movement
    • Rings
      • Array of independent times sequences
      • Traffic Lights – Fixed Time Control
        • “Electromechanical signal controllers”
          • Timers used that have fixed intersection schedules
            • Length of period determined by gears
              • 35-120 seconds
    • Set time plans, thus, can not adapt to flow of traffic

2 Types of Systems
  • Traffic Lights – Dynamic Control
    • Central programme which sets limits
    • Input: detectors
      • Sensors: signal if vehicle is on road
        • Needed for adjustment of signal timing & phasing
        • Used to award longer time for green light, or less time dependent on how heavy the traffic is
        • 3 types
  1. In-pavement
    1. Underground
    2. Uses detector loops à change of magnetic field (like metal detector)
    3. Runs along with default timer, which is used for vehicles with less metal
    4. Non-intrusive
      1. Over-road
      2. Either use: sound sensor, electromagnetic waves or video processor
      3. Advantages:
i. Cheaper than in-pavement
ii. Less effected by environmental degradation
iii. Allow real-time management
iv. More data types collected
  1. Detection of non-motorized vehicles
    1. Pedestrians, bicycle riders, etc.
    2. Pedestrian buttons removed, now incorporated with timing of traffic à detected through sound
    3. For bicyclists à special, sensitive in-pavement control
  • o Coordinated System
    • Controlled by master controller
      • Set up so there is progression of green lights
      • Advantages:
        • Speed limit implemented à lights timed in a way that a very low speed can be maintained (“green wave”)
  • Synchronized System
    • All change at same time
    • Used in older systems

Conclusion: How does a traffic light control system work?

  • Is an open-loop system

  • How?
  1. Sensor detects car
    1. input
  2. Sends signal over wireless connection
  3. Microprocessor receives input - calculates - produces output
    1. Decision based on density of traffic (quantifiable data received as input)
    2. Also length of green period based on traffic density
      1. Measures as high, medium, low density which has corresponding time assigned
  4. Sends signal for switching
  5. Signal sent over malfunction management unit (MMU)
    1. Checks whether signal possible (e.g. all green not possible)
    2. Fail - proof time schedule system in place
  6. Signal transmitted to traffic light
    1. Output

Special software used à transmission signals within microcontroller, which represent a ‘high’/’1’ means light goes green

Discussion of how the control system works
The government, in order to control and enable safe traffic, implements the control system. The system discussed is a dynamic control systems, as the output in terms of the length of the green phase is adjusted due to traffic density, measured in the 3 values: high, medium, low. There are other types of traffic control systems too, like the timed one. This is less advanced, as traffic is not considered, but traffic lights merely turn green or red for a certain time period.

Firstly, an input is recorded by wire in the ground responding to a disturbance in the magnetic field. This disturbance is a response to the car entering the magnetic field. There are other possibilities of receiving an input. For example, infrared cameras can determine the density of the traffic too, as well as sound sensitive systems in place.

The input come in form of quantifiable data determining whether the traffic density is high, medium or low. The input is sent to the microprocessor over wireless or cable to the central processor unit (there are several units located in the city). The processor then considers the density of the traffic for the different traffic lights. The light with the highest density is queued first. Furthermore, the density of traffic not only defines the order, but also the length of the green phase. A signal, the output, is sent to according traffic lights. This signal contains the information of whether the specific light should turn green or stay red. The output is sent to the traffic light over the malfunction management unit, which ensures that failure cannot happen. The MMU checks whether the combination of lights is logically possible. In worst-case scenarios, a predefined red-green phase scheme is started, that has fixed time limits for the green phases.

traffic light.jpg

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Interesting Idea:
  • Audi Travolution Project
  • (Check it out here!)
    • Communication between light and car
      • Light would signal how long till next green phase, so car can adjust speed
      • Display how much time left to wait until turns green
      • Advantage
        • Increase safety
        • More efficient use of petrol
Created By: Lucie Charlotte Magister
Last update: 11/12/2014