Apparatus for detecting defective conditions associated with a set of railway vehicle wheels and with a railtrack upon which a given railway vehicle travels comprises a rotation measurement unit for generating data indicative of rotational rate of the set of wheels; a motion sensor, such as an accelerometer or vibration sensor, for generating data indicative of motion along a vertical axis relative to the railtrack; and a data processor coupled to the motion sensor and to the rotation measurement unit for receiving the rotational rate and motion data. The data processor is designed for detecting, based on the received rotational rate and motion data, a defective condition associated with the wheel set and for detecting, based on the received motion data, a defective condition associated with the railtrack. The apparatus can be operatively combined with a mobile tracking unit for a vehicle tracking system.