Condition monitoring of railway tracks is essential in ensuring the safety of railways. In-service vehicles equipped with sensors and GPS systems can act as probes to detect and analyze real-time vehicle vibration. Such trains are known as "probe vehicles". Recently, a compact size on-board sensing device has been developed. This paper describes the track condition monitoring system using the compact size on-board sensing device and the diagnosis software. The diagnosis software provides a function to detect track irregularities using RMS of the car-body acceleration. It also provides a function to analyze in time-frequency domain using wavelet transform. Monitoring experience in a local railway line showed that the system is effective for practical use.
