Estimation Method of Equivalent Units for Entering Vehicles at Highway Accesses

Equivalent units of vehicles are important parameters for road capacity and service level analysis. However, due to the fact that our country's existing road network has not yet included access roads into the technical grade system and lacks corresponding design specifications and technical standards, access points often have great impacts on highway traffic operations. Based on the characteristics of different types of vehicles at the highway entrance, this paper analyzes the physical significance of occupying space-time resources of lanes on the highway section under different traffic flow statuses when the vehicle at the access point enters the highway section. Furthermore, taking the passenger car as the standard vehicle, estimation models for equivalent units of vehicles at the highway and the access point are proposed respectively. Finally, the UAV aerial photography is used to collect field data, and an access point on Zhengzhou G107 with multiple vehicle types is used as an example for empirical analysis. Calculation results show that: (1) At the access point, the equivalent unit of each entering vehicle type increases with the increase of road traffic; and the more lanes occupied during the entry process, the higher the vehicle equivalent unit. (2) At the access point, the equivalent unit of each vehicle type increases first and then decreases with the increase of the traffic flow speed on the highway section, which shows a boundary around 40km/h. That is because, in the steady flow state between the free flow and the saturated flow, the headway is between that of the free flow and that of the saturated flow. The vehicle at the access point is more convenient when driving into the highway section, but it affects many vehicles on the road highway. At this time, the vehicle equivalent unit is also large.