When rails become rusty, the short-circuit impedance becomes higher, making it difficult for the track circuit to detect a train exactly. This is a problem of the rail-wheel contact system. However, we have found that the waveforms of track circuit signals usually become distorted when the short-circuit impedance is higher. Thus, we can detect the train by checking the distortion of the waveforms of the signals, even when shunting conditions are not good. This paper describes the algorithm of this train detection method and the result of field tests.

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