## 5 Shapley Explanation for the Relationship between Micro-Behavior and Geometric Design
### RF-SHAP Analysis of Mirco-Behavior on Combined Curves
#### 5.2.2 Lane Departure Behavior on Downslope, Upslope, and Crest Curves  
Three types of lane departure behavior were modeled separately: the direction of centrifugal force (IDCF) and against the direction of centrifugal force (ADCF) were modeled separately.  
(1)Downslope Curve  
The _MAE_ for the RF model on IDCF lane departure behavior in the downslope curve is 0.2108. Figure 12 shows the SHAP values for the geometric design parameters of the downslope curve.  
From Figure 12, the design parameter that has the greatest impact on the IDCF for the downslope curve is \(G_{mean}\). The SHAP values of \(R\) and \(L_{cc}\) are next to \(G_{mean}\). Other geometric design parameters have a relatively low impact compared to the \(G_{mean}\).  
Figure 11: The SHAP values for adjacent alignment geometric design parameters of sag curves.  
The _MAE_ of the RF model of ADCF lane departure behavior in the downslope curve is 0.2468. Figure 13 displays the SHAP values for the geometric design parameters of the downslope curve.  
Figure 12: The SHAP values for the geometric design parameters of IDCF lane departure behavior on downslope curve.  
Figure 13: The SHAP values for the geometric design parameters of ADCF lane departure behavior in downslope curve.  
According to Figure 13, the \(\Delta G\) of the SHAP value for slope difference is the largest at 0.050. The SHAP values of \(L_{dt}\) and \(L_{cc}\) are next to \(\Delta G\). The \(L_{at}\), \(R\), and \(G_{mean}\) have less effect on the ADCF lane departures on downslope curves.  
1. Upslope Curve
2. Upslope Curve
3. The _MAE_ for the RF model on IDCF lane departure behavior in the upslope curve is 0.2363. Figure 14 shows the SHAP values for the geometric design parameters of the upslope curve.  
From Figure 14, the design parameter that has the greatest impact on the IDCF lane departure behavior of the upslope curve is \(R\). Other geometric design parameters have a relatively lower impact compared to the radius.  
The _MAE_ of the RF model of ADCF lane departure behavior in the upslope curve is 0.2747. Figure 15 displays the SHAP values for the geometric design parameters of the upslope curve.  
According to the Figure 15, the \(\Delta G\) of SHAP value for slope difference is the largest at 0.1243. The SHAP values of \(L_{cc}\) and \(R\) are next to \(\Delta G\). The \(G_{mean}\) and \(L_{at}\) have less effect on the ADCF lane departures in upslope-curves.  
1. Crest Curve
2. The _MAE_ for the RF model of IDCF lane departure behavior in crest curves is 0.2619. Figure 16 shows the SHAP values for the geometric design parameters of crest curves for IDCF lane departure behavior.  
Figure 14: The SHAP values for the geometric design parameters of IDCF lane departure behavior on upslope curve.  
Figure 16: The SHAP values for the geometric design parameters of IDCF lane departure behavior on crest curve.  
Figure 15: The SHAP values for the geometric design parameters of ADCF lane departure behavior on upslope curve.  
From Figure 16, it is evident that \(L_{cc}\), \(\Delta G\) and \(L_{dt}\) have the greatest influence on the IDCF lane departure of the crest curve.  
The _MAE_ for the RF model of ADCF lane departure behavior in crest curve is 0.2146. Figure 17 shows the SHAP values for the geometric design parameters of crest curves for ADCF lane departure behavior.  
From Figure 17, the parameters that have the most influence on the ADCF lane departure of the crest curve are \(L_{cc}\), \(\Delta G\), and \(L_{dt}\).