In Japan, there is a huge number of short- and medium-span bridges in service, and it is becoming a major social concern how these bridges can be maintained in good condition during their whole lifetime. In this paper, we propose a method for assessing the condition of existing short-span (10–20 m span length) reinforced concrete bridges based on data obtained by monitoring public bus vibrations. This paper describes the details of not only a prototype monitoring system using information technology and sensors, which is capable of providing more accurate knowledge about bridge performance than traditional ways, but also a few specific examples of bridge condition assessment using public bus vibrations measured when driving on bridges, based on the data from the system.