### TRAFFIC APPLET

This simple model illustrates the behaviour of traffic.

A circular road is depicted as a series of 100 spaces, each with room for one car, the cars proceed according to the (simultaneously applied) simple rules:

1. A stationary car has a 50% chance of moving forward if there is a free space ahead. Moving cars keep moving if there is a free space ahead.
2. The applet shows moving cars in yellow, stationary ones in red. You can choose how may cars are on the road - if you only have one it moves freely, if you have 100 nothing moves.
You might think that with 50 cars, they could organise themselves so that there was a space ahead of each all the time: if you set up this situation, it works, but if you perturb it, you find it is unstable.

Try 45 cars. Look at the applet - what happens is immediately clear, traffic jams form (red cars), move backwards along the road, and eventually coalesce. Now, you can study the size and velocity of the traffic jams as a function of number of cars.

The cars are moving anticlockwise on the road; you can change the probability that a stationary car moves off if there is a free space ahead.

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