Bridges as one of the important infrastructures are suffering from many defects during their
service lives. In our country, because there are a huge amount of existing short and medium span bridges in
service, it is becoming one of major social concern how those bridges can be maintained in good condition
during their whole lifetime. In this paper, a method of the condition assessment is proposed newly for existing
medium & short span RC bridges based on monitoring data from public bus vibration. 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 of bridge performance than traditional ways but also a few specific
examples of bridge condition assessment by public bus vibration measured in operating on the bridge
based on the data from the system. This paper also describes a sensitivity analysis for deteriorating bridges using
the city bus acceleration response by using "substructure method" based on finite element model for verification
of the above mentioned results of bridge performance.