Currently, a lane imbalance design scheme without auxiliary lanes for two-lane exits is increasing. To study the rationality of this exit scheme, the relationship between lane balance and traffic efficiency in the diverging area is investigated using a drone and image recognition software. The Kalman filter is used to optimize the original data and simplify the process of extracting the traffic volume, density and speed by Frenet coordinate transformation. Under the three states of free flow, saturated flow and supersaturated flow, lane balanced exit and lane imbalanced exit simulation models were constructed by using VISSIM. Based on the traffic flow theory, the curve of the relationship between traffic volume and density was fitted. The traffic volume corresponding to the difference between two schemes at the same density not exceeding 5% or 10% is calculated, and this traffic volume is defined as the scheme selection limit value. The results show that the traffic efficiency of lane imbalance scheme is consistently lower than that of lane balance scheme under all traffic conditions at the freeway exits. However, the difference in traffic efficiency between the two schemes is not fixed but increases as the upstream input traffic volume increases. When the exit forecast service traffic volume is lower than the " scheme selection limit value " (SSLV), the difference in traffic efficiency between the two schemes will not exceed 5% or 10%. In conclusion, the lane imbalance scheme can be used in the diverging area under certain traffic volume conditions, thus reducing the land, engineering volume and cost requirements. It also provides ideas for the study of three-lane exit ramp design schemes.