Experimental investigation of vibration sources and transmission in subway turnout zones under diverging routes with small-radius curves

Train passage through turnouts induces significant vibrations in urban rail transit systems, particularly under diverging-route operation with small-radius curves. Such curves generate pronounced centrifugal forces, amplifying structural responses. To investigate vibration sources and transmission characteristics of turnouts, full-scale field tests were conducted for both through and diverging routes. Vertical and lateral accelerations were measured at rails, track slabs, and tunnel walls. Time–frequency analysis was applied, and new indicators were developed to quantify vibration transmission efficiency and energy distribution in the variable cross-section turnout. Vehicle–turnout rigid–flexible coupled dynamic simulations were used to interpret the observed vibration behavior. Results show that diverging-route vibrations are dominated by low-frequency components (1–30 Hz) induced by centrifugal forces, with higher amplitudes than in through-route operations. Vertical vibrations exhibit higher transmission efficiency than lateral vibrations. These findings highlight the mechanisms of low-frequency vibration generation and provide guidance for vibration control in urban rail turnout zones.