## 1 Introduction  
With the continuous growth of economic development and travel demand in recent years, the traffic volume of some freeways tends to be saturated, making it difficult to manage traffic and ensure driver safety. Compared to newly built roads, reconstruction and expansion projects have the advantages of short construction periods, low costs, and less land occupation, and have gradually become a new trend in freeway construction. Work zones for reconstruction and expansion construction often occupy the shoulder or part of the lane, reducing the number of lanes available to drivers and traffic capacity within the area zone, which can cause traffic congestion [1; 2]. At the same time, road and traffic conditions and driving behaviors are constantly changing, leading to increased traffic safety risks [3; 4]. Compared to 10 years ago, in 2021, fatal crashes, fatalities, and estimated injuries in U.S. work zones increased by 56.9%, 54.4%, and 35.5%, respectively, and the accident rate in work zones is 3.36 times that in non-work zones [5]. Thus, traffic safety problems in work zones urgently need to be solved. Some scholars have studied traffic safety problems in work zones [6; 7], and their results indicate that in addition to driver factors, changes in driving behavior due to changes in construction zone configurations and road traffic conditions are one of the main causes of accidents [8; 9]. Most work zones must occupy the shoulder or part of the lane in order to ensure proper construction, resulting in a decrease in the number of lanes available to drivers, and a transition area is set up to allow vehicles to change lanes and merge with adjacent normal traffic lanes to cross through the work zone. If the transition area length is short, the speed of the vehicles is too low, and the speed difference compared to adjacent lane vehicles is large, which can cause rear-end collisions and other accidents when merging [10; 11]; moreover, it is difficult for vehicles to complete lane changing and merging within a transition area of limited length, which can lead to traffic congestion [12]. If the transition area length is too long and the speed of vehicles is too fast, drivers will find it difficult to react in a timely manner when road and traffic conditions change, which will likewise increase the road safety risk [13], work zone length, and construction costs. [PERSON] et al. analyzed the characteristics of accidents in work zones in Virginia, and their results indicated that the proportion of vehicles involved in side-collision accidents in the transition area was significantly higher than in other areas of work zones [14]. [PERSON] et al. used a machine learning method to analyze traffic conflicts in work zones and non-work zones under different traffic conditions. They found that changes in speed and acceleration were primary reasons for traffic conflict, and conflict probability can be effectively reduced by changing the transition area length and increasing the angle between the vehicles [15]. Therefore, clarifying the impact of transition areas on traffic and driving behavior characteristics in work zones, and determining the optimal length and layout of transition areas, represent the foundations for improving traffic efficiency and ensuring traffic safety. Some scholars have also conducted research on traffic characteristics and transition area length. In terms of traffic and driving behavior characteristics in transition areas, [PERSON] et al. used vehicle trajectory data to analyze the speed-traffic volume relationships in nine areas, and proposed a speed prediction model for work zones. It was found that the transition area had a significant impact on the speed of vehicles from 200 m upstream of the transition area to the activity area, and the impact on different lanes and vehicle types varied [16]. [PERSON] et al.