The permanent way of these service roads is generally made as simple as possible. A pair of movable rails are used instead of switches, as shown in Fig. 60. These rails are linked together by iron tie-rods, and pulled or pushed over into position for one or other of the roads 70 by means of the handle at A. A stout iron pin, or iron clamping-plate, serves to retain the rails in position during the passing of the waggons. In a similar manner, a short rail working on a pin, or pivot, is made to answer the purpose of an ordinary crossing. The rails are laid complete and continuous for the one road, and for the second road the outer rail is laid sufficiently high to cross over the rail of the first road. A piece of rail is then secured by a centre pin, or pivot, to the cross-sleeper, as shown on Fig. 61. This pivoted rail is pulled over into the position shown by the dotted lines, to allow the passage of waggons on the one road, or pulled across to the end of rail at B, for waggons to pass on or off the other road. In the latter case an iron pin or clamp serves to keep the pivoted rail in position. As these service roads are merely laid down on the soft loose material brought forward for filling, they require constant packing and lifting to prevent them working into depressions, which might cause the waggons to leave the rails. To indicate the height of the embankment filling, strong stakes or poles must be firmly set in the ground at each chain-peg. On each of these poles two cross-bars must be fixed, the lower one placed to the correct height of the embankment, and the upper one to show the amount allowed for subsidence. The excavated material, as brought from the cuttings, is in a soft, loose condition, and an allowance must be made for its settlement, or subsidence, as the embankment becomes consolidated. This allowance will, of course, depend on the height of the embankment and the quality of the material, but for ordinary earth and clay it is customary to allow about one inch to the foot of height, which is equal to about 8 per cent. When forming embankments over very side-lying ground, it is necessary to cut steps in the sloping surface on which the filling material has to be placed, as shown in Fig. 62. These steps give a hold to the new earthwork, and check the tendency to slide down the hillside. Embankments have frequently to be carried over ground which is low, soft, and wet, but not boggy. If the culverts and drains are sufficiently large, and properly arranged, these places are not likely to cause much future trouble.