It is demonstrated that negative entropy flow exists in shock wave and shock wave is a kind of heat wave which transfers heat with traveling wave velocity.

So, this paper can discriminate the state of road traffic. The negative entropy flow model can ensure the extent of traffic management and the best management time should be taken when road is crowed.

Based on the thermodynamics entropy, this paper discusses the way to build up the traffic flow thermodynamics entropy, and establishes the traffic flow entropy model.