This paper reports on the feasibility study of damage identification of a bridge by the bridge displacement estimated from the responses of a passing vehicle over the bridge. The road roughness in the measument may be cancelled by averaging the obtained displacement, provided that the roughness is randomly given at every run of the passing vehicle. Based on the obtained displacement of the bridge, the second order differential of the bridge displacmenet is evaluated to identify the damage. As a result of numerical verification, at least the average over 500 times should be used to identify the damage and the sensivity of the damge identification depends on not only the degree but also location of damge. For further research, the assumption that a roughness is given at random should be evaluated by experiment in the filed.
