## 2 Literature Review  
### Problems in Small Spacing Distance Interchange  
An interchange is an area with a high incidence of accidents, and when interchanges are dense, more problems will arise. In the process of diverging and emerging, the impacts will extend to a certain distance upstream and downstream. The research found that the diverging impact area ranges from the diverging point to 1000 m upstream, and the emerging impact area is from the emerging point to 350 m downstream [6]. Therefore, when the interchange spacing is small, the diverging influence area at the downstream interchange exit will overlap with the emerging influence area at the upstream entrance. This overlap creates a complex traffic environment [18]. Generally, exit signs are set 0.5 km, 1 km, and 2 km before freeway exits. When the interchange spacing is small, the cue signs for different ramps will overlap, leading to difficulties in information recognition for drivers. As a result, vehicles tend to concentrate on changing lanes near the exit [19]. In addition, a major factor that seriously affects traffic efficiency is the weaving behavior of vehicles when the spacing between interchanges is small. The part between the entrance of the previous interchange and the exit of the next interchange creates a weaving area where vehicles change lanes with increased frequency. As a vehicle needs to exit the freeway, it typically needs to transition to the outermost lane in advance. This lane-changing process can have a significant impact on some aspects, including the distribution of vehicles, operating speed, and headway. When vehicles are affected by lane-changing behaviors, they become more vulnerable to traffic accidents [20; 21]. Different weaving distances significantly impact accident rates, with short weaving areas having become accident-prone zones [21]. Increasing weaving distances can improve the driving environment when drivers change lanes continuously, thus reducing the frequency of collisions [2]. By studying the operational characteristics of vehicles in the weaving area, it has been observed that most lane changes occur within the initial half of the weaving area or even change lanes immediately after entering the weaving area; the weaving area is not fully utilized, resulting in serious traffic congestion [22; 23; 24]. From the perspective of traffic psychology, drivers who need to exit will change lanes as soon as possible after entering the weaving area. This behavior is driven by the desire to avoid missing the exit due to a delayed lane change. Moreover, as traffic volume increases, so does the level of psychological tension and urgency experienced by drivers. This leads to the concentration of vehicles changing lanes in the weaving area. The weaving area becomes a bottleneck section because of the diverging and emerging behaviors, which affect the operational efficiency of the freeway. Even in situations with low traffic volume, the weaving area tends to exhibit poor operating conditions [25]. Therefore, by distributing lane-changing behaviors evenly within the weaving area, congestion and safety problems caused by concentrated lane-changing can be effectively improved [26]. Currently, traffic volume is increasing rapidly, and freeways are facing or have completed reconstruction and expansion projects to accommodate the growing demand by increasing the number of lanes. For small spacing interchanges, it is more difficult for vehicles to change lanes. Drivers are unable to find a suitable gap for lane changes before the diverging area, resulting in forced lane changes or even stops close to the diverging point. As a result, this leads to a significant increase in traffic conflicts. It has been found that the main cause of accidents occurring in the weaving area is attributed to forced lane changing. This behavior becomes particularly prominent when the interchange spacing is too small [4]. It is worth noting that this hazardous behavior tends to occur near exit ramps.