# 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
In this study, a time to collision (TTC) below 3 s was categorized as a potential risk, and TTC exceeding 4.4 s was classified as high risk. Hence, a reciprocal of less than 0.333 s for TTC indicates low risk, while over 0.2273 s signifies high risk [34]. Traffic laws in different countries have different definitions of \"safe headway\". Some driver training programs in the United States consider it unsafe to follow a vehicle for less than 2 s. In Germany, it is stipulated that the front distance must be more than half of the speed (1.8 s at 80 km/h [35]). According to a controlled experiment published in the literature [36], when the time headway is greater than 2 s, the probability of no traffic accident occurring is actually greater. On the contrary, the smaller the headway, and at less than 2 s, the more likely that there is no actual traffic accident. In accordance with the literature [37], when there is a risk of conflict between road vehicles, the headway time-distance between them is essentially distributed within 2 s. When the time gap between vehicles is greater than 5 s, the risk of collision is the least likely. Therefore, the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Input Variable** & **Meaning** & **Correlation Coefficient** & \(p\) **Value** \\ \hline v\_vel & Vehicle speed & 0.235171 & 8.8057353\(\times\) 10\({}^{-29}\) \\ \hline v\_Acc & Vehicle acceleration & \(-\)0.095398 & 0.0 \\ \hline Space\_Hdwy & Headway spacing & 0.063748 & 8.928308 \(\times\) 10\({}^{-136}\) \\ \hline Time\_Hdwy & Headway time distance & \(-\)0.046715 & 1.5712488 \(\times\) 10\({}^{-61}\) \\ \hline \(\Delta Y\) & Relative position to the center of the intersection on the yaxis & 0.041653 & 47.9663287 \(\times\) 10\({}^{-34}\) \\ \hline \(\Delta V\) & Relative speed & 0.555878 & 3.1486108 \(\times\) 10\({}^{-27}\) \\ \hline \(\Delta Acc\) & Relative acceleration & 0.008949 & 0.0 \\ \hline TTC & Time to collision & 0.038922 & 5.582351 \(\times\) 10\({}^{-24}\) \\ \hline \(1\)/TTC & Inverse of time to collision & 0.165755 & 0.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristic variable definition and correlation analysis. risk threshold for headway time-distance in this work was set according to the above standards. More specifically, a headway greater than 5 s is low-risk, a headway less than 2 s is high-risk, and a headway between 2 s and 5 s is medium-risk. For the quantitative expression of the time-headway parameter, the headway time-distance of adjacent vehicles was set to \(T\). When \(T>5\) s, it is quantified as 1. When 5 s \(>T>2\) s, it is quantified as 2. When \(T<2\) s, it is quantified as 3. The degree of conflict between adjacent vehicles is reflected in the collision hazard posed by vehicles. According to the criteria in the literature [37] (100-vehicle naturalistic driving tests), a vehicle has a high collision risk of 3 if the driver must slow down the vehicle by more than 5 to avoid a collision. If the risk is 2, the vehicle needs to decelerate at a speed of [2; 5] since the driving state of the vehicle is in a critical safety state. If it is 1, the vehicle slows down when the speed is less than 2, and the current driving situation is safer. This paper mainly evaluates the risk of lane changes by processing the NGSIM dataset. The characteristic parameters, such as 1/TTC, Space_Hdavy, v_Acc, \(\Delta Acc\), and others, for lane-changing vehicles were obtained. Through [PERSON]'s correlation analysis, strong correlation variables were eliminated, and five factors representing the vehicle collision risk situation were obtained. In addition, specific quantification and risk threshold divisions are shown in Table 2.