Track irregularities in monorail tour-transit systems: Field measurements, spectral patterns, and dynamic impacts

Track irregularities critically impact ride comfort and structural safety in monorail tour-transit systems (MTTS), yet field measurements and corresponding spectral analysis remain limited. This study establishes a systematic framework for evaluating track irregularity conditions and their dynamic effects in MTTS, integrating field measurements, spectral characterization, and numerical validation. The first comprehensive measurements of longitudinal and cross-level irregularities were conducted across eight operational MTTS lines. Subsequent analysis revealed distinct spectral patterns that fundamentally differ from those of conventional railways, with short-wavelength irregularities (0.1–1 m) exhibiting particularly significant influence. A five-grade assessment system (Classes A–E), based on root-mean-square thresholds across critical wavelength ranges (0.1–1 m, 0.1–30 m, 0.1–60 m), was developed to provide practical evaluation criteria. Most notably, coupled numerical simulations demonstrated that track irregularities significantly amplify track beam deflection, increasing the peak response by 1.22 × and the vibration amplitude by 6.63 × —an impact far greater than that of operational speed. These findings provide an essential track irregularity database for further numerical studies and offer direct guidance for optimizing MTTS design and maintenance protocols.