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Cross Section of Side-Hill Streets

street, curb, level, fig, slope, line, difference and elevation

CROSS SECTION OF SIDE-HILL STREETS. The arrange ment of the cross section of a street upon a side hill is a matter re quiring good judgment, that needless damage may not be done to the abutting property or that the general appearance of the street may not be uselessly sacrificed. In solving this problem no fixed rules can be laid down; but each case must be treated by itself, taking into account the local conditions. Fig. 90 shows the nor mal arrangement for a residence street on level ground; both footways are at the same elevation, the slope of the parking is the same on the two sides, the tops of the curbs are at the same level, the gutters are of the same depth, and the surface of the street rises equally from each side to the center. The normal section for a business street would be the same except that the sidewalk would occupy all the space between the curb and the building line. On a side-hill street the above conditions can not always be realized; and various expedients must be resorted to, depending u2on the difference in elevation of the two sides of the street. The following are some of the common expedients.

1. If the difference is. not very great, the curbs may be set at the same level, and one sidewalk may be placed higher than the other, the grade of the parking being different on the two sides. On a business street, where there is no parking, the slope of the footway may be different on the two sides. With sidewalks consisting of stone slabs, cement, or asphalt, a slope of at least I of al inch per foot (1 in 96) is required for drainage, and a slope of more than 1 of an inch per foot (1 in 32) is dangerous when covered with ice or snow.

2. A slight difference of level may be overcome by raising the curb, i. e., by increasing the depth of the gutter, on the low side, and lowering the curb on the high side, the crown of the pave ment remaining symmetrical about the longitudinal center line. Fig. 91 shows an actual section of a street arranged on this plan.

Except under extreme conditions, the curb should not show more than 10 inches because of the difficulty of stepping to or from the pavement, nor less than three inches because of the danger of its being overflowed when the gutter is full of melting snow.

Sometimes a double curve is employed with a horizontal tread about 1 foot wide between the two risers. The combined con crete curb and gutter (§ 522) lends itself most readily to this form of construction. Fig. 92 shows such an arrangement.* The ob

jections to the double curve are: 1, its cost; 2, the difficulty of keeping the step neat and sanitary; and 3, it lessens the width available for roadway and sidewalk. In practice these objec tions have not proved to be serious. Instead of the double curb, it has been proposed to place the second step at the area line or property line, to which arrangement the owner is liable to ob ject, particularly on a business street.

3. A slight difference may also be overcome by making the upper side of the pavement nearly level and giving the lower half the normal slope.

4. The crown may be moved toward the high side of the street, the profile for each side being determined in the usual way; that is, the surface of the pavement may be two planes meeting at the crown with the intersection rounded off a little, or it may be two arcs of a circle or a parabola tangent to a horizontal line at the high point (see § 310 and § 512). Fig. 93 is an actual example of this method of solution.* If the longitudinal grade is consid erable, as it usually is under such circumstances, there is no objec tion to the upper side of the street's being exactly level transversely. The extreme of this solution is to make the surface of the pave ment a right line from the upper to the lower side—see Fig. 94. This arrangement has been objected to on account of its throw ing all of the drainage to one side of the street; but this is not a serious objection, particularly if there is a considerable lnligitudi nal grade, as there is usually.

5. Where there is a considerable difference of elevation on a residence street, it is sometimes wise to place the footway next to the curb, and to allow the slope of the parking to unite with that of the property—see Fig. 95.

6. When any or all of the above solutions fail, it may be neces sary to terrace the street and to construct an upper and a lower roadway as shown in Fig. 96.

When the street contains one or more street-ear tracks, the problem of arranging a cross section on the side of a hill is still more complicated. It is necessary that the two sides of a track shall be at least nearly on the same level; but it is not necessary that the two tracks shall be at the same elevation. A difference in elevation of I of an inch between rails of the same track and of 3 inches between adjoining tracks is permissible.