=Endwalls for Culverts.=--A substantial retaining wall is placed at each end of the culvert barrel, whatever the type. This is to prevent the end of the culvert from becoming choked with earth and to retain the roadway at the culvert. It also indicates to the drivers the location of the end of the culvert. The endwall extends a foot or more below the floor of the culvert to prevent water from cutting under the barrel. Plain concrete or stone masonry are most commonly used for culvert endwalls. [Illustration: Fig. 4.--Two Types of Drop Inlet Culvert] =Reinforced Concrete Box Culverts.=--The pipe culvert is limited in application to the smaller waterways. Reinforced concrete is extensively used for culverts of all sizes, but especially for the larger ones. These are usually constructed with endwalls integral with the barrel of the culvert. Culverts of this type must be designed for the loads anticipated to insure suitable strength and stability, and must be constructed of a good quality of concrete. Figs. 2 and 3 show designs for pipe and box culverts. [Illustration: Fig. 5.--Drop Inlet Culvert] =Drop Inlet Culverts.=--In some locations erosion has begun in the fields adjacent to a culvert and it will probably continue until the stream above the culvert has eroded to about the level of the floor of the culvert. This is a reason for placing the culvert as high as the roadway will permit, so long as the area above the culvert will be properly drained. Considerable reclamation of land is possible if the culvert is constructed with a box at the inlet and as shown in Fig. 4. The area up-stream from the culvert will not erode below the level of the top of the box at the inlet end. Where the stream crossing the road has eroded to considerable depth or has considerable fall, as would sometimes be the case on side hill roads, the culvert barrel would follow the general slope of the ditch but should have a drop inlet. This type of culvert is shown in Fig. 5. CHAPTER IV ROAD DESIGN =Necessity for Planning.=--Sometimes highway improvement is the result of spasmodic and carelessly directed work carried out at odd times on various sections of a road, finally resulting in the worst places being at least temporarily bettered. The grade on the steepest hills is probably reduced somewhat and some of the worst of the low lying sections are filled in and thereby raised. Short sections of surfacing such as gravel or broken stone may be placed here and there. From the standpoint of the responsible official, the road has been "improved," but too often such work does not produce an improvement that lasts, and sometimes it is not even of any great immediate benefit to those who use the roads. In nearly every instance such work costs more in money and labor that it is worth.