Abstract: A theoretical framework is developed to describe the evolution of modal frequencies and damping ratios of vehicle–bridge interaction (VBI) systems. Analytical solutions are derived and validated against finite element results, with the effects of the vehicle–bridge frequency ratio, mass ratio, damping ratio, and relative vehicle position systematically examined, along with the governing mechanisms near resonance. Key findings include: the frequency and damping ratio exhibit markedly different variation patterns near resonance; for a simply supported beam, the bridge frequency attains its extreme value at midspan, governed primarily by the vehicle–bridge frequency ratio; when the mass ratio is much less than unity and the damping ratio exceeds unity, the bridge damping ratio reaches its maximum at midspan, indicating a vehicle-induced damping enhancement effect; as the mass ratio increases, this maximum damping ratio can be reduced to the minimum, with the maximum values shifting symmetrically to both sides of the bridge.