The diagram below depicts a one-lane ring road with four segments. It can be animated to describe the physics of gridlock. Click "Play" button below at any time to start.

• Four entrances are designated by the spurs on the circle. Vehicles (not shown) are queued waiting to enter. When released, entering vehicles claim the right of way and appear in the ring as colored dots.
• Each entering vehicle is randomly assigned a destination/exit color: red, blue, yellow, green .
  When a vehicle arrives at its destination (square of the corresponding color), it exits.
• Cumulative exit counts for each color/destination are shown by the columns to the right of the circle. .
• The exit rate is shown in the center of the circle. This measures the system's productivity.
• Goal: achieve the highest exit rate , thus the greatest productivity.
• Click here to see the controls explained in detail.