# Prototype Network for Few-Shot Hazard Assessment of Vehicle Lane Changes in Risk Field
## 2 Analysis of Lane-Change Behavior and Data Extraction
### Influencing Factors and Quantification of Indicators  
The spatio temporal relationship between vehicles can be applied to judge the degree of danger and study the risk factors under different lane-change conditions. The element set of the hazard posed by vehicle collision can be divided into a conditional attribute set (including the driver factor [C1], vehicle factor [C2], surrounding vehicles of the vehicle SV factors [C3], and decision attribute set (including the hazard posed by lane changes [d]). Among them, the driver factor [C1] includes the left lane change (LCL) and right lane change (LCR). Since the risk of LCL is lower than that of LCR during normal driving, the behavior was quantified as 1 for the LCL and 2 for the LCR. The vehicle factor [C2] includes variables such as the local vehicle speed, local vehicle acceleration, and transverse-longitudinal displacement. The factors for the vehicles surrounding vehicle SV [C3] include 1/TTC (the inverse of time to collision), Time_Hdwy (time headway), and Space_Hdwy (spacing headway), as shown in the Equation (4). \[\left\{ \begin{array}{ll}\mathbb{TTC}_{a}=\frac{\{local_{gu_{a}}(t)-local_{gu _{b}}(t)\}}{v_{b}(t)-v_{a}(t)},&v_{b}(t)>v_{a}(t)\\ \infty,&v_{b}(t)\leq v_{a}(t)\\ \mathbb{Time\_Hdwy}=\frac{local_{gu_{a}}(t)-local_{gu_{b}}(t)}{v_{a}}(t)\\ Space\_Hdwy}=local_{y_{b}}(t)-local_{y_{a}}(t)\end{array} \right. \tag{4}\]  
where \(v(t)\) represents the vehicle speed and \(local_{y}(t)\) represents the distance of the longitudinal position of the vehicle at time \((t)\). The hazard posed by lane changes [d] is divided into high risk, medium risk, and potential risk. In this study, data extraction was carried out using pre-processed data to obtain detailed information such as the speed and the acceleration of the current vehicle  
Figure 3: Data comparison of vehicle speed (**a**) and time headway (**b**) before and after filtering. and the vehicles in front of, behind, and ahead of the target lane. The indexes related to the risk evaluation of lane changes were obtained. First, the obtained data were analyzed using correlation to determine the most reliable indicators of the model. Through the above introduction, a total of nine variables related to vehicles were obtained. Then, Pearson's correlation analysis was performed for the risk-free and at-risk datasets. The results are shown in Table 1. Six variables with a high correlation were selected based on correlation coefficients. In addition, all _p_-values were less than 0.05, indicating a significant correlation. After the elimination of the variable with a strong correlation, relative vehicle speed, only five vehicle parameters remained as inputs for the risk prediction model. TTC (time to collision) [30] can indicate the relative speed and distance between the lane-changing vehicle and the target vehicle, a metric often used in analyzing longitudinal collision safety in vehicles. According to [PERSON] et al. [31], TTC tends to infinity when the speed of the leading vehicle exceeds that of the following vehicle in the same lane. Both vehicles continue to drive in their current conditions with a minimal risk of collision. At this point, the TTC value can be consistently set to 30 s. This study utilized [PERSON]'s method to calculate the vehicle's TTC value during driving. If the leading vehicle in the same lane was moving faster than the following vehicle, the TTC value was set to 30 s. When the speed of the vehicle ahead in the same lane was inferior to that of the vehicle behind, the relative distance and relative speed between the two vehicles were used to ascertain the TTC value. Furthermore, an analysis of the TTC value was conducted if the quotient exceeded 30 s. [PERSON] et al. [32] proposed classifying a time to collision (TTC) within 3 s as high risk and TTC exceeding 5.5 s as low risk. [PERSON] et al. proposed using the median and the 85 th percentile to categorize the risk thresholds, defining TTC under 2.1 s as low risk and TTC over 4 s as high risk [33].