<p>Viaduct structures, which are girders supported on piers, are essential for high speed railway (HSR) lines to ensure uninterrupted flow in densely populated regions. Owing to dynamic amplification of deformations and forces, which can be severe under resonant conditions, and the need to limit deck acceleration for structural safety, passenger comfort and rolling stock performance, dynamic analysis is imperative in the design process. Current design standards provide little guidance regarding dynamic analysis approaches, and the research literature indicates that the options are Euler–Bernoulli beam modal analysis, Kirchhoff–Love plate theory-based Generalised Beam Theory (GBT) modal solutions, and finite element (FE) based time domain approaches. This paper investigates the applicability of the simple beam modal solutions on four representative viaduct sections under three typical axle load sets, operating between speeds of 200 to 350 km per hour. First, eigenanalysis solutions using GBT and a solid FE model are compared, indicating excellent agreement under an idealised simply supported boundary condition with torsional restraint, but significant deviations when the FE boundary is modified to represent realistic bearing-type restraints. These observations propagate to dynamic responses under high speed train loading, which generally show good agreement for the analytical boundary condition and differences under realistic boundary condition modelling. Although analytical predictions are typically conservative, the FE predictions are at times significantly higher due to a shift in resonant speed. The results indicate that simplified analytical solutions can be utilised with caution and should be conducted at all applicable speeds to capture the maximum plausible resonant response. The paper concludes with a discussion on its limitations and future research needs.</p>