S Khezri - Ph.D student, Kharazmi University, Tehran, Iran
F Hosseinzadeh - Department of Mathematics, Science and Reaserch Branch, Islamic Azad University, Tehran, Iran
M Najafizadeh - Ph.D student , Shahid Beheshti University, Tehran, Iran

Data Envelopment Analysis, is a branch of management, concerned with evaluating the performances of homogeneous Decision Making Units. Usually increases in inputs cause increases in outputs. However, there are situations where increase in one or more inputs generate a reduction in one or more outputs. In such situations there is congestion in inputs or production process. In this paper, we consider directional congestion and we propose some algebraic equations and linear programming models which in addition to measuring the directional congestion. Moreover, we suggest methods for determining the existence of the directional congestion when only one direction of input or output is given, also our method can determine the other direction.

Data Envelopment Analysis (DEA); Directional Congestion; Decision making Units