• • Field validation on an 18-span, 609.5-m simply supported HHR bridge identified five interlayer damage locations, demonstrating the method's capacity to localize defects across multiple spans without fixed sensors.
• • The IAQI indicator, derived from Hilbert transform of axle box acceleration, enabled damage localization even when beam damage, track irregularity, and noise were simultaneously present, reducing false positives from sleeper-passing frequency components.
• • The hybrid filtering approach, combining bandpass filtering around sleeper-passing frequencies and a statistical diagnostic tool, successfully discriminated interlayer damage from normal sleeper-related driving responses, a critical bottleneck in drive-by inspection.
• • When wheel entry/exit responses are unavailable, the method permits conservative evaluation using the nearest pier response, ensuring detection continuity for locations near span ends (e.g., location 6) and maintaining inspection reliability.