A traffic jam is a situation in which transportation networks such as roads or highways become obstructed by cars or trucks, because drivers are in the incapacity to move any further away their vehicle.
A traffic jam can be a real puzzle to solve for road agents in charge of relieving congestion in a road, even if the traffic is blocked on a small portion.
Little by little, the flow of cars increases, provoking a snowball, or cascading effect: extra cars going into the road are restrained to slow down and to queue.

There are many of reasons converging in such a mess.
First of all, when the number of cars attempting to go into a road is too high compared to the capacity of the road to be occupied by such a volume of vehicles.
It is characteristic of urban areas: cities attract lots of people who go to work, and who take their cars at the same time, because of office hours.
Then, when roadworks form a neck, narrowing the passage of cars on a road. Finally because of accidents.

It is difficult to predict a traffic jam and some people see in them a manifestation of the butterfly theory. Let's say that it's raining, and that someone - usually a train commuter- decides to drive to go to work. The problem is that many people has had the same idea. Let's say that the traffic suffers at first from lower speeds, and that our fellow man is in a hurry. Then, let's say that he does something stupid, like attempting to run a red light and that a motorbike comes from a junction, obliging our driver to pull over abruptly. Then, he'll probably lose the control of his car, because the rain makes more difficult this kind of maneuverer.

Such an accident at peak time leads to traffic jams: policemen must secure and delineate an area around the place where the accident occurred. A detour for cars can even be determined.

France holds the record for longest traffic jams. This reputation has been fostered when on February 16, 1980, drivers were trapped in a congestion long of 176 kilometers...