Abstract: Wheel/rail contact state is the basic content in analyzing safety of the train, and the relative
displacement between wheel/rail is the most direct reflection of wheel/rail contact state. The current
contact measurement based on sensor is widely used in dynamic performance parameters detection
for monitoring locomotive status. However, it has several defects, such as being difficult to realize
dynamic measurement and has poor anti-jamming capability. In order to overcome the defects above,
the video monitoring system for wheel/rail relative vertical displacement is designed in this paper. In
the system, camera and laser are installed on the bogie vertically. Since the camera, laser and bogie
remain static each other, then the wheel/rail relative vertical displacement can be measured by the
laser ordinate change in image. Finally, the experiments had been carried out under the two different
conditions of ballastless track and ballast track. The results show that the system can acquire
wheel/rail vertical relative displacement and has strong adaptability to the detection environment, and
it has great important significance to further exploring and evaluating locomotive safety mechanics.

Key words: wheel/rail contact status, wheel/rail vertical relative displacement, locomotive safety