1. Origins of congestion

1.1 Position and definition of the problem

Two key concepts help us understand the phenomenon of congestion: traffic supply and demand. These are local notions that determine, respectively, the actual maximum flow that can flow downstream and the actual maximum flow that is desired from upstream.

The notions of supply and demand are related to the notion of infrastructure capacity, which defines the theoretical maximum flow that can circulate locally on the section under consideration. Capacity is an upper limit to supply and demand. The congestion that every user has experienced is mainly due to a situation where supply is lower than demand. The volume of vehicles wishing to flow cannot therefore be satisfied.