Research Conclusions： For the structures over the railway with low net height which can not meet the requirement for two layer container convey , special structure treatment scheme of contact line will be considered at the first place on condition that the main technical standards of the existing railways are not be lowered. If it is impossible to use special contact line scheme to solve the problem, lowering the level of railway, lifting or rebuilding the existing structure over the railway will be considered. Temporary line and measurement can be considered when it is difficult for the reconstruction of the existing railway so that the existing mainline can be shut down for the reconstruction of level lowering of the existing line. The height of the lowerest point of contact line on the two Iayer container passage will be 6 250 mm. At the place where it is not allowed to raise the line level, the height of the lowerest point of the contact line on the two layer container passage can be 6 200 mm. The height of the hanging point of contact line will be 6330mm normally.