A Shinkansen overlap is a device for sectioning the overhead contact line mechanically and electrically and is set up at intervals of about 1.5 km (Fig. 1). Since the trolley wire in the pantograph transition segment at an overlap section tends to wear out more easily than that in other sections, such pantograph transition segments represent maintenance weak points, leading to more frequent replacement of the trolley wire.
      Conventionally, the cause of wear is assumed to be the excessive contact force generated when a pantograph passes an overlap, and modification of the height structure of trolley wire led to some improvements. However, it has been impossible to stop the progress of wear completely.
      The Railway Technical Research Institute (RTRI) has examined the cause of wear from a different perspective. The examination showed that there is a correlation between the wear rate of trolley wire at an overlap section and the deviation in the direction perpendicular to the trolley wire. The wear rate becomes particularly large when the deviation exceeds 150 mm, which is the standard zigzag deviation in the general section (Fig. 2). This is probably caused by the intermittent sliding (at intervals of about 1.5 km) of the slider and trolley wire.
      As a countermeasure, the deviation at overlap sections was adjusted to fall within about 150 mm, leading to the reduction of the wear rate to the level of that in the general section (Fig. 3).
      This countermeasure is applicable to all overlap sections except air sections (i.e.about 80% of all overlap sections).