In this paper, we design the vehicle tracking in the terahertz (THz) vehicle-to-infrastructure (V2I) networks, where roadside units (RSUs) equipped with leaky-wave antennas help to estimate the driving states of multiple vehicles after receiving the vehicles’ feedback. Different from the conventional phased arrays, the leaky-wave antenna has the potential of improving the sensing accuracy with lower system overhead thanks to its unique spatial-spectral coupling feature. The generalized mobile scenario is studied in which vehicles drive at time-varying speeds. A novel unscented Kalman filter (UKF) based solution is proposed to track the vehicles without requirement of addressing the Doppler effect. Simulation results confirm that the proposed tracking solution can evaluate the propagation angle, vehicle’s states and inter-vehicle distance accurately.