Abstract: In order to study the influence of built environment on the walking time of the elderly considering different travel purposes, the extreme gradient boosting tree model (XGBoost) was constructed by using Shantou resident travel survey data in 2021, to analyze the non-linear relationship between the built environment and the walking time of the elderly. Combined with SHAP algorithm, the relative importance of variables and overall interpretability was output. The research results show that the goodness of fit of the model is higher after classifying travel purposes. The importance of the number of household bicycles increases significantly for survival travel, while the importance of the number of cars decreases. The importance of normalized difference vegetation index (NDVI) is highest for living travel, while the importance of all other built environment variables increases. The number of bus stops and land use mixing degree have a “V”-shaped relationship with walking time of the elderly, with the effective influence range of 5~13 and 0.40~0.80 respectively, and both the number of bus stops above 10 and land use mixing degree above 0.70 can promote walking time of the elderly. The number of intersections has a significant positive impact on NDVI overall, but NDVI exhibits a threshold effect, with a corresponding threshold value of 0.33. The research results can provide a theoretical basis for improving the aging-friendly environment of community construction and formulating transportation policies for the elderly.

Key words: traffic and transportation engineering; elderly; travel purpose; built environment; non-linear relationship; XGBoost model

摘要： 为研究不同出行目的下建成环境对老年人步行时间的影响差异，采用2021年汕头市居民出行调查数据，构建极端梯度提升模型（XGBoost）分析建成环境对老年人步行时间的非线性关系，结合SHAP算法输出变量相对重要度和总体可解释性。研究结果表明：划分出行目的后模型的拟合优度更高。生存性出行时家庭自行车数量的重要度显著提高，而小汽车数量重要度下降；生活性出行时归一化植被系数（NDVI）重要度最高，此时其他建成环境变量重要度均提升；公交站点数量和土地利用混合度与老年人步行时间存在“V”形关系，其有效影响范围分别为［5, 13)和(0.40, 0.80)，公交站点数大于10和土地利用混合度大于0.70均可促进老年人步行时间；交叉口数量和NDVI总体上具有显著正向影响，但NDVI表现出阈值效应，其对应阈值为0.33。研究结果可为社区建成环境适老化改善和老年人交通政策制定提供理论依据。

关键词: 交通运输工程；老年人；出行目的；建成环境；非线性；极端梯度提升模型