The interior infrasonic level in a bus is an important factor that may affect the driver and the passengers. Scientists have found that high infrasound noise can have an effect on disorganizing nervous activities in a similar manner to the effects of alcohol. This may bring potential safety risk to driving. However, attention has traditionally focused on audible noise inside various modes of transportation. There has been very little spectral data reported at infrasonic frequencies for noise inside busses. In view of this, this article applies to study of infrasound signals generated by running busses. Tests were carried out on 15 busses, three groups divided according to their used time. After measurement, the time-domain signals were transformed into the frequency-domain by using the Fast Fourier Transform (FFT), the main characteristics of bus generating infrasound were discussed in terms of the frequencies. Data derived from measurements were compared with the limits specified in existing standards and/or regulations in this field in order to evaluate the effects that bus generating infrasound may cause.