In this paper the general concept of entropy developed in physical is applied to forecast the transportation process parameters in a city or a broader region. The expression for entropy is obtained by generalization of the classical Hamilton's principle of the smallest action as the most general formulation of the movement of mechanical systems. The practical example of the application of this example of this concept to the real system, a medium sized city, shows that the approach presented in this paper gives quite good and useful results, and can be used for solution of various planning problems in transportation networks.