## 4 Data Description
### Model Formulation  
The threshold of TTC usually ranges from 2 s to 4 s in previous studies [9; 45]. Considering that the ETTC is an extension of the conventional TTC, the threshold of TTC also applies to ETTC. In this study, 4 s is selected as the threshold for ETTC as it could contain more potentially risky cases. Dividing the safety status of vehicles into conflict and non-conflict only may ignore the severity of the conflict, which leads to the safety analysis lack of details. Classifying the severity of traffic conflicts between vehicles could assess the state of traffic safety status more accurately. Conflict severity is often divided into multiple categories with an intrinsically ordinal structure, and thus the ordered-response model may be a promising alternative to account for this characteristic [9; 41; 46]. Therefore, in this study, the conflict risks of different ETC and MTC vehicle-following patterns are divided into three levels: (1) The most severe conflict risk level, indicating a high possibility of collision (ETTC less than 2.5 s). This risk level applies to situations in which a collision will occur if the driver does not take prompt action immediately; (2) The medium risk level, which represents that the two vehicles have the potential for collision but drivers have sufficient reaction time to avoid the collision (ETTC between 2.5-4 s); and (3) The lowest risk level (ETTC larger than 4 s), which represents that the distance between the two vehicles is large enough so that it is nearly impossible to collide. Figure 4 depicts the frequency and proportion of observations for each level of conflict risk. Vehicle-following patterns with the same toll collection types (ETC-ETC, MTC-MTC) have a higher percentage of most severe conflict risk. The MTC-ETC vehicle-following pattern has the highest percentage of slightest conflict risk and the lowest percentage of the most severe and medium risk levels. To fully explore the differences of conflict risk among different parts of the diverging area, the diverging area is divided into 12 sub-segments. As depicted in Figure 5, the length of each sub-segment is 30 m, numbered from 1 to 12. The first ten sub-segments are in the non-lane marked area, while the last two sub-segments are within the lane marked diverging area. The candidate variables used in this study are listed in Table 1. The variables considered in the model can be categorized into three groups: (1) location-related variables, mainly including the position features of the following vehicle during the whole diverging process at each time step; (2) speed-related variables, the average speed and acceleration of the following vehicle in each sub-segment, and the whole diverging process at each time step; (3) traffic environmental variables, mainly including the conflict risks of vehicles around the following vehicle in the same sub-segment at each time step. Figure 4: The distribution of conflict risk levels in four vehicle-following patterns. Specifically, in traffic environmental variables, considering the mixed travel of MTC and ETC vehicles is the main feature of the TMTP, the entropy index \(Z_{\text{MIX}}\) was developed to assess the mixed degree of MTC and ETC vehicles in each sub-segment. Moreover, the length of conflict duration has been proven to be an essential index for analyzing the safety state of a vehicle as the start and end of a collision is a continuous process [26]. Thus, this study applies the time exposed to collision (\(T_{\text{TEC}}\)) to the candidate variables.