###### Abstract  
Interchanges are the key nodes of the freeway. Due to the existence of weaving behavior, the traffic flow situation is more complicated for small spacing interchanges. Continuous auxiliary lanes are usually used to connect the entrance and exit to form a compound interchange to reduce the interference of weaving behavior. However, when it comes to the design of auxiliary lane forms, China lacks relevant design specifications and research in this area. As a result, there often exists the phenomenon of mismatch between the design form and the traffic volume. In this paper, we took a compound interchange in Xi'an as the research object, proposing four auxiliary lane design schemes and using VISSIM (2022 student) software to establish the simulation model. Additionally, various traffic conditions were simulated through sensitivity analysis. Finally, using the factor analysis method and entropy method, we comprehensively assigned weights to the indexes. By obtaining the weighted scores for various schemes, it became possible to determine the applicability of each scheme under different traffic conditions. The results indicate that the gradient auxiliary lane can be applied to most traffic conditions and has a smaller land occupation than the traditional design, which is an optimization and improvement for the traditional design form. keywords: freeway; compound interchange; auxiliary lanes; factor analysis method; entropy method; VISSIM +
Footnote †: journal: Applied  
Due to the unique operation mode of interchanges, vehicular behavior exhibits notable deviations from that observed on the basic mainline sections. Therefore, over-intensive interchanges will significantly impact the operational condition of vehicles. However, the limitation of distance should not impede the development of freeway construction. In order to solve the problem of spacing between interchanges, the most efficient solution is to connect two interchanges. The widely adopted method is to connect the interchanges with auxiliary lanes or collector-distributor lanes. However, in China, land restrictions are relatively strict, and the implementation of collector-distributor lanes will occupy more land. As a result, auxiliary lane connections are predominantly used for small spacing interchanges in China. To achieve this, additional lanes are incorporated outside the outermost lane, connecting the entrance and exit ramps. This configuration forms a compound interchange, effectively shifting the weaving behavior to auxiliary lanes. As a result, the normal flow of the mainline straight traffic remains unaffected. This paper collects traffic volume data from a typical compound interchange in Xi'an. We select four auxiliary lane forms for modeling, calibration, and simulation in VISSIM, using eight indexes of delay, mainline travel time, CO emissions, fuel consumption, number of conflicts, TTC, PET, and CSI as evaluation indexes. Finally, based on the factor analysis method (FAM) and entropy weight method (EWM), the auxiliary lane forms are compared under different traffic volumes, diverging, and emerging rates. The EWM is a method of comprehensive evaluation by assigning weights to different indexes. The EWM has a wide range of applications in many fields, such as environment [11], physics [12], and transportation [13]. The FAM is a method to explore the hidden relationship of several variables and then extract common factors and obtain the optimal solution. The FAM is extensively utilized in the transportation field [14], including identifying the factors affecting accidents in freeway construction areas [15], predicting the severity of freeway accidents [16], and researching road factors that lead to the use of mobile phones while driving [17]. Currently, the configuration of auxiliary lanes connecting interchanges lacks uniformity in China. The relevant norms and standards do not provide specific guidelines, and the design of auxiliary lane configurations lacks reliable research.