Because too many persons interested in the source code for this applet, I have added it to the ZIP files you will receive when you click "GET APPLET FILES" button. It was written 8 years ago with JDK1.0.2 The physics behind the code is very simple. Just car with constant acceleration (a) when car is accelerated. When the car reach maximum velocity, it will move with the same velocoty (acceleration a=0 ). There is a minimum distance between any two cars to avoid collision between two cars. When there is a red light or if the distance between two cars is less than minimum distance, the car will slow down (another constant acceleration: -a). I hope the above information is helpful for those who want to do more work on the code. I am sorry that I did not add enough comment in the code. Fu-Kwun :-)