This study establishes a series of “indirect” identification frameworks to estimate the bridge frequencies by processing the dynamic response of traversing vehicles. Specifically, this study applies general system identification techniques, namely subspace identification, to the vehicle-bridge interaction (VBI) problem.Firstly, the study verifies the stochastic subspace identification (SSI) with a realistic VBI model and discusses the effect of the road surface conditions (RRCs), vehicle speed, and regular on-going traffic. Numerical experiments show that the SSI method can effectively identify bridge frequencies when RRC is good. The on-going traffic can amplify the bridge vibration and facilitate the identification of higher modes of the bridge. However, the SSI method only allows low vehicle speed (about 1.39m/s=5km/h) that conceals the time-varying nature of the VBI system.