Management of the existing traffic network and understanding current traffic conditions is the most important and effective way to solve traffic congestion. This research investigates the status of Korea expressway through the Speed-Flow-Density diagram and finds the best suitable queueing model for each area. Dynamic structure in the queueing model enables us to reflect the structural change of the road in case of traffic congestion. To find the best model and estimate the parameters, we use the Newton-Raphson method. Finally, we examine the road efficiency in view of the optimal speed and density using the conditional distribution of speed and density of a S-F-D diagram.