Low-cost carriers vs. high-speed rail? Difference in passenger's travel preferences in Shanghai and Chengdu

High-speed rail (HSR) and low-cost carriers (LCCs) have emerged as increasingly prominent modes of intercity travel, particularly in rapidly urbanizing regions. Understanding the determinants of passengers' mode choices is essential for informing transportation policy, optimizing infrastructure investments, and enhancing the overall travel experience. This study employs a stated preference (SP) survey to investigate these determinants in two distinct urban contexts: Shanghai and Chengdu. A total of 494 valid responses were collected in Shanghai and 524 in Chengdu, capturing data on sociodemographic attributes, attitudinal dispositions, and travel-related characteristics. To analyze this dataset, we integrated machine learning techniques with the SHAP (Shapley Additive Explanations) algorithm, enabling both high predictive accuracy and interpretability. Three models—random forest (RF), support vector machine (SVM), and eXtreme Gradient Boosting (XGBoost)—were evaluated, with the RF model demonstrating superior performance. This model was subsequently used to interpret the relative importance of influencing factors. The findings reveal that factors associated with HSR travel, such as service frequency, ticket price, and in-vehicle travel time, play a vital role in passengers' mode choice. Regional contrasts also emerged: passengers in Shanghai exhibited a stronger preference for LCCs, while those in Chengdu were more inclined toward HSR, particularly among price-sensitive travelers. Interestingly, travelers who prioritize safety, comfort, and convenience tended to favor LCCs in both regions, suggesting a shifting perception of LCC quality and reliability. Finally, this study presents targeted recommendations for both government and operators, focusing on enhancing market transparency, maintaining fare stability, adopting region-specific strategies, and improving safety, comfort, and convenience. The findings offer theoretical insights into the mechanisms driving passengers' choices between HSR and LCCs, along with practical implications for policymaking and strategic optimization.