Service Scale and Level: How Origin–Destination Interactions Shape Intercity Travel Flows Within Mega-City Regions

As regional integration and high-speed transport networks advance, intercity travel flows within mega-city regions (MCRs) provide a lens for understanding regional functional division of labor and spatial organization. Concentrated high-intensity flows between core cities and major peripheral nodes suggest that explanations should move beyond distance constraints and single-end city attributes to origin–destination functional linkages. Consumer and producer services help connect these functional linkages with actual travel flows, yet existing studies have focused mainly on service scale and paid insufficient attention to service level, which reflects functional non-ubiquity and diversity. This study incorporates service type, scale, and level, and origin–destination relationships into a unified framework to identify key factors associated with intercity travel flows within MCRs. Focusing on the Yangtze River Delta, this study examines subdistrict/town-level flows from 15 peripheral cities to Shanghai’s central urban area. Mobile phone signaling records measure flow intensity. Counts and complexity are used to measure service scale and level. Two XGBoost models are estimated: an origin–destination service model and a difference model. SHAP identifies contributions and directions, while two-dimensional ALE examines interactions between services at origins and destinations. Results show that both service scale and level are associated with intercity travel flows within MCRs, but their patterns differ by service type. Significant interaction effects exist between services at origins and destinations. These interactions mainly combine origin-scale foundations with destination-level-based attraction, with destination service level often showing threshold-like characteristics. This study extends the explanation of intercity travel flows to origin–destination functional linkages and service level.