DRAINAGE, ROAD-CROSSINGS, ROAD-DIVISIONS, ETC.
Drains.—To lead off the watercourses that intersect the road, suitable provisions must be made by means of structures that will vary according, to the size and direction of the stream and the nature of the available building material. Where the amount of water to be carried across the road is very small, drain-pipes constructed of cast iron, earthenware, cement, asphaltum, etc., may be made use of for the purpose (1./. 26, figs. 7, 8). The ends of these drains are commonly built in with masonry floor and side walls and provided with a pit of masonry at the entrance, to serve as a mud-receptacle. Covered drains of masonry are used for watercourses of somewhat larger volume (figs. 9, To).
the stream to be spanned is still larger, arched cul verts (figs. II, 12) are resorted to, the arches of which are given usually a covering- of cement or asphaltum, to protect them against the infiltration of moisture from the overlying- material of the embankments. Where the descent is comparatively steep (figs. T3, 14), the floor of the drain or cul verts is sometimes stepped; but this arrangement, which conducts the water by a series of cascades, is apt to be severe on the masonry. The smooth pavement in the form of a flat inverted arch is given commonly the preference. Special care must be observed to secure unyielding founda tions under high embankments, lest the superincumbent weight should cause settlement or distortion of g-round by lateral pressure.
Guticrs.—Where the vertical distance from the bottom of the creek or ri-vtilet and the road-surface is insufficient to permit of a covered drain or culvert, an open glitter is formed, in which case either the two adjacent cross-ties rest on the stone side walls, or, if the drain be too wide, the track is supported on iron carriers resting on the walls. As, on the one hand, the arched drains, by increasing dimensions, gradually develop into stone bridges, so, on the other hand, the carriers over the open drains may be looked upon as iron bridges in miniature.
railway necessarily intersects many roads, public and private, which for convenience of travel must be left open. In all
cases where this is practicable, and especially in cities and towns, such crossing-s should not be made at grade, but should be carried either above or below that of the railway. In Europe, where many of the railways are operated by the government, a much more excliusive control of the road way is exercised than in the United States. Trespassing on the tracks is forbidden, under penalty, and road-crossings are everywhere carefully guarded. Should the road and the railway be on the same level, or should there be a slight difference in height, requiring trifling modification by levelling, a crossing is commonly made at grade, which crossing—at least, on principal lines—it is the custom to provide with a gate or other safe guard that inay be closed to prevent accidents while trains are passing the point.
To avoid railroad-crossings at grade, the railway must be made either above or below the highway. Where the railway is an elevated crossing, the depressed highway resembles the arched or open drains above men tioned, except that the floor is arranged as a highway with the necessary width. Elevated crossings are viaducts of wood, stone, or iron furnished with one or more openings, according- to the width of the roadway. Depressed railway-crossings are usually seen where the railroad passes through cuts or between embankments. Even in cases where the con formation of the ground would make crossings at grade the easier and cheaper course, overhead crossings are considered preferable, because they are safer and require no attendant to guard the place. The rapid growth of a multitude of towns and cities along the lines of railways extending into new territory is responsible for the very general existence of grade crossings. Crossings at grade are rapidly disappearing- from the more important cities, but in a great number of situations, unfortunately, they still prevail, and they will disappear only when the inconvenience and the danger resulting from them become insupportable.