The train-detecting track circuit currently used is dependable and has the characteristics required of a railway signalling system in terms of economy, continuous detection, etc. However, when rails become rusty, the shunt resistance becomes higher, making it difficult for the track circuit to detect trains precisely. We have therefore researched shunting malfunction to enable the proposal of a new countermeasure against the phenomenon. In this paper, we describe the measurement and analysis of environmental conditions and resistance. We then show the results of these experiments, and propose that shunting malfunction is a problem of railway systems as a whole that should be addressed through the adjustment of the various conditions involved.