The stray current in urban rail transit will cause different degrees of electrochemical corrosion to the surrounding metal facilities.And the transition resistance of rail to ground is the key factor to control the scale of stray current.This paper tries to explore a measurement method of the transition resistance by studying the spectral characteristics of the mutual impedance between the tracks.Firstly

a subway rail simulation model is established to obtain the influences of rail short-circuit location

soil resistivity

and transition resistance on the spectral characteristics of the mutual impedance of two rails.A method for using the mutual impedance to identify the rail-to-ground transition resistance is put forward.It is found that:1) Rail short-circuit wiring affects the spectrum characteristics of the mutual impedance in low frequency section

and the closer the short-circuit wiring is to the measuring point

the greater the impact becomes;2) When the short-circuit wiring is 500 m away from the injection point

the measurement frequency needs to reach more than 4 kHz;and 3) Most of the effect of soil resistivity on the spectrum characteristics of the transition resistance occurs below 100 kHz.By comparing the proportions of the mutual impedance at different frequencies and the mutual impedance at 50 Hz

it is concluded that when the value of the impedance ratio is greater than 18.2 at 100 kHz or above

the transition resistance is considered less than 3 Ω·km.This study suggests that the rail-to-earth transition resistance can be detected by the spectrum characteristics of rails ’ mutual impedance

which provides a new idea for the detection of the transition resistance in urban rail transit.