A traffic status evaluation method of expressway merging area based on improved coupling theory

Abstract

In order to further reveal the law and characteristics of on-ramp traffic flow into the main line of expressway road and make up for the deficiency of traditional inflow model which cannot evaluate the state of merging area, the coupling theory in physics was introduced. First of all, “gap acceptance” model was adopted to describe the operation law of merging area, and the relationship between important parameters such as flow rate and headway was analyzed by using discrete probability function. Second, coupling degree and coupling coordination degree were put forward, after analyzing the characteristic under the premise of the merging area, using a large amount of measured data regression analysis of the traffic, location speed and the headway of parameters in the coupling. The coupling theory was modified, the coupling function evaluation model of confluence area was established, and the interaction and influence between main line and ramp system were quantitatively analyzed and evaluated. Finally, the model is verified by the actual observation data of Shanghai expressway. The results indicate that in the early peak period, the coupling coordination degree is about 0.36 and 0.4, which is in a moderate coordination stage. During the peak flow period, the coupling coordination degree is only 0.28, which is in a low degree of coordination coupling and the system is relatively disordered. In nonpeak hours, the coupling coordination degree is around 0.83, which is in an extremely coordinated state. The error between the flow calculated by the coupling theory and the data observed in the field is generally 4.2%–12.8%, which indicates that the results of the running status evaluation of merging area by using this model are reliable.