The Biham–Middleton–Levine traffic model is a cellular automaton that represents a flow of traffic.
The concept is simple:
Pixels represent cars
They are two types of cars:
Cars that move downward
Cars that move rightward
Car types take turns:
All downward cars move
Then all rightward cars move
Then all downwards cars move again
And so on...
Cars only move if their future spot is vacant
Cars of their type only move all at once