Three-phase traffic theory is a theory of traffic flow developed by Boris Kerner between 1996 and 2002. It focuses mainly on the explanation of the physics of traffic breakdown and resulting congested traffic on highways. Kerner describes three phases of traffic, while the classical theories based on the fundamental diagram of traffic flow have two phases: "free flow" and "congested traffic". Kerner’s theory divides congested traffic into two distinct phases, "synchronized flow" and "wide moving jam", bringing the total number of phases to three: