In many cases for village streets, where the traffic is light and it is essential that the cost of construction be low, it may be good practice to construct the traveled portion of the roadway of macadam, or other ment, and use cobble gutters at the sides without curbs. Fig. 33 shows a roadway 3o feet wide, with macadam middle and cobble gutters. In Saginaw, Mich., this method has been followed, using either macadam or wood blocks for the middle portion, and in the report of City Engineer Roberts for 1893 it is recommended as economical and efficient.
The cross-section of streets must be arranged with reference to proper surface drainage. The street is given a crown at the middle to throw the water into the gutters, and sidewalks usually have a sufficient in clination toward the gutter to cause them to drain over the curb. The crown necessary to insure good drain age in the roadway depends upon the nature of the covering, being less as the surface is more smooth and less permeable to water. For macadam roadways, it may vary from about 4 to of the width of the roadway. For the various pavements, the required crown varies from about sa to rhb of the width, accord ing to the smoothness of the surface and the permea bility of the construction. For brick, asphalt, or wood-block surfaces, a crown of from $a to rsa of the width is commonly ample. Stone blocks may need slightly more; while, on streets of considerable longitudinal slope, the crown may be made somewhat lighter.
The form of section is usually a convex curve, sometimes circular but more often parabolic, the para bolic curve differing but slightly from the circular. This form is shown in Fig. 34. The distance of the curved surface below the horizontal through the highest point is proportional to the square of the horizontal distance from the center. Thus, if the distance A —D
be divided into 3 equal parts, the vertical distance from B to the curve is one-ninth and from C four-ninths of that at D.
The street is usually made practically level across, the curbs and sidewalks at the two sides being given the same elevation. The parking at the sides may have a slope between the sidewalk and the building-line when it is necessary or advantageous. Sometimes, on streets along a slope, expense may be saved or adjoining property benefited by placing the sidewalk at a dif ferent elevation from that of the street, as shown in Fig. 5, or by placing one curb lower than the other and moving the crown of the road to one side, as shown in Fig. 35.
The surface drainage of alleys is secured either by forming the section as in a street, with a crown at the middle and gutters and curbs at the sides, or, as is com monly preferable with narrow alleys,- by placing the gutter at the middle and sloping the pavement from the sides to the center. Where the gutter is in the middle it is common to make the bottom of the gutter of a flagstone 15 to i8 inches wide. Fig. 36 shows a center-drained alley with block-stone pavement upon sand foundation.
The form shown in Fig. 36 is also usually employed where concrete pavement is used for alleys,, as is quite common. This is desirable in many instances on ac count of the good drainage afforded, and the resistance of the material to dampness.
Fig. 37 shows a side-drained cobble pavement for an alley. These have been extensively used in the past, being usually placed upon sand foundation. They are gradually being replaced by brick or concrete pave ments.