This study is intended to assess the low frequency sound radiated from a viaduct which was solicitous about the low frequency sound at the design stage. This paper discusses about a field experiment focusing on the low frequency sound radiated from a viaduct which comprises wide cantilever steel decks and steel box girders. Analytical results taken from a traffic-induced vibration analysis and boundary element method are also discussed. Observations demonstrate that analytical sound pressure levels in frequency domain show similar tendency with those of experimental ones, even though analytical results do not perfectly match with experimental ones. The propagation of the sound pressure taken from the analysis reveals that the distribution of the sound pressure level at lower frequency below 10Hz is greatly affected by the vibration of bridge's entirely motion. On the other hand, those SPL over 10Hz is affected by vibrations of the bridge decks.