Skip to main content

Why Kathmandu traffic lights are open loop

Short answer

The traffic light system in Kathmandu is open loop because it operates on fixed timers without sensors measuring actual traffic flow. There is no feedback of output (queue length) to adjust the light timing, so it cannot correct for disturbances.

Why do you think traffic light system in Kathmandu is an open loop control system?

The traffic-light system in Kathmandu is open loop because its control action (which light is on and for how long) does not depend on the output (the actual traffic flow or queue length). The lights change according to a timer that is set in advance.

 timer     +------------+  lights  +---------+ vehicle flow
 setting ->| Timer/     |--------->| Traffic |------------>
 (fixed)   | controller |          | (plant) |
           +------------+          +---------+

Reasons

  1. No feedback sensor: there are no vehicle detectors (loops, cameras) feeding traffic data to the controller.
  2. Fixed time sequence: green, amber and red times are preset; an empty road gets the same green time as a crowded one.
  3. No comparison with a desired value: the controller has no error signal; it cannot know whether the queue is growing.
  4. Disturbances are not corrected: a sudden rush, accident or VIP movement is not handled automatically. In practice traffic police switch to manual control, which itself shows the automatic system has no feedback.

To make it closed loop, sensors would measure queue length or waiting time, and an adaptive controller would adjust the green time accordingly.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Control Systems chapter 1 questions →