Wheel flats, caused by the braking of rolling stock, give rise not only to vibration and noise of vehicles but also to mechanical damage to bearings and axels. The actual conditions of wheel flat occurrence were investigated for commuter trains running on main lines by means of a wheel skid detector newly developed by the authors. Places and times at which wheel skids frequently happened on a JR line were clarified as a result of the investigation. The phenomenon and mechanism of wheels being locked by electric braking were discussed as major factors for flat occurrence. The decrease in adhesion between rails and wheels at such locations was evaluated under various climatic conditions.
