# The Nonlinear and Threshold Effect of Built Environment on Ride-Hailing Travel Demand
## 5 Results and Discussion
### SHAP Summary Plot of Independent Variables  
The SHAP summary plot reveals the order of various built environment features and how they positively or negatively influence the target variable. In the plot, each colored point corresponds to a sample, with the color indicating the magnitude of the built environment feature values. Higher feature values are depicted in red, while lower feature  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Variables** & **Relative Importance** & **Ranking** \\ \hline Density (average of relative importance: 7.89\%) & & \\ Population density & 1.36\% & 15 \\ Dining facility & 30.75\% & 1 \\ Company & 5.94\% & 4 \\ Shopping facility & 4.86\% & 5 \\ Financial facility & 26.42\% & 2 \\ Accommodation service & 3.19\% & 7 \\ Science, education, and culture & 1.34\% & 16 \\ Semic spot & 0.59\% & 18 \\ Commercial residence & 3.56\% & 6 \\ Leisure service & 2.55\% & 9 \\ Medical facility & 6.28\% & 3 \\ Design (average of relative importance: 1.86\%) & & \\ Road length & 2.07\% & 10 \\ Non-motorized road length & 1.88\% & 11 \\ Number of road nodes & 1.63\% & 13 \\ Diversity (average of relative importance: 1.48\%) & & \\ Land use mix & 1.48\% & 14 \\ Destination accessibility (sum of relative importance: 3.05\%) & & \\ Distance to CBD & 3.05\% & 8 \\ Distance to transit (average of relative importance: 1.53\%) & & \\ Distance to bus stop & 1.23\% & 17 \\ Distance to subway station & 1.82\% & 12 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The relative importance of independent variables.  
values are depicted in blue. The \(x\)-axis illustrates the SHAP values corresponding to each built environment feature.  
As shown in Figure 2, based on the SHAP feature ranking, it is found that the top four ranked built environment features are similar to the relative importance ranking, all of which are POI facilities, namely dining facilities, financial facilities, companies, and medical facilities. Among them, dining facilities are considered the most important, with the highest contribution to relative importance ranking as well. However, the road length is ranked fifth in the SHAP feature ranking, which differs from the relative importance ranking.  
Samples with fewer dining facilities tend to have negative SHAP values, while samples with larger dining facilities tend to have positive values, indicating a positive correlation between dining facilities and SHAP values. This is because areas with higher-density dining facilities often coincide with shopping malls or densely populated areas, resulting in higher travel demand. Similarly, POI facilities such as finance facilities, company facilities, medical facilities, shopping facilities, accommodation facilities, and leisure facilities also exhibit similar feature effects, while tourist attraction POI show negative effects. The distance to the CBD and subway accessibility are negatively correlated with SHAP values, indicating that closer proximity to the CBD results in higher travel demand. Similarly, other built environment variables that exhibit significant negative correlations with SHAP values include the distance to subway station. Road length and the number of road nodes show positive correlations with SHAP values. Conversely, the non-motorized road length shows a negative correlation. This is because road nodes enhance the connectivity of urban roads, and a more complete and smooth road network structure attracts more ride-hailing travel demand [22]. Conversely, a focus on non-motorized transportation development will reduce motorized travel and suppress the demand for ride-hailing travel demand.