This paper reports the stochastic characteristics of identified frequencies in the laboratory test of a bridge–vehicle interaction. Three states (one intact and two damaged) are assumed, and the paper focuses on the occurrence histogram of dominant frequencies obtained by the autoregressive method. A rotational support is immobilized for one damaged state and distributed mass is added to the model beam for the other damaged state. The measurement test is repeated 300 times to obtain enough data to assess the statistical characteristics of the identified frequencies of a passing vehicle and of the bridge. Results show that the bridge frequency merges into the vehicle’s interaction frequencies, but the histogram of the identified frequency (including the merged frequencies) depends on the states and, in particular, their variances differ even when the mean values are almost identical.