At intersections the crown of the roadway pavement on each street should, if possible, be continuous to the center of intersection, in order to prevent vehicles on one street from being subjected to the jar incident to passing over the gutter of the other. Where a storm sewer is available into which the water from the gut ters on the upper side can be emptied this is a simple matter, but where such sewers do not exist it requires the adoption of some special means of draining the gutters on the upper side. This may sometimes be accomplished by a culvert across the street, the gutters being somewhat depressed at the corners to bring the channel sufficiently low. In other cases, where the slope is sufficient, it is more satisfactory to construct an underground pipe-drain from the upper corner to some point in the gutter below the crossing.
Where the rate of grade is such that it is feasible, it is desirable that the grade of both streets should be brought to a level at intersections. The top of the curb at the four corners should be at the same elevation, thus permitting the continuation of the full section of each roadway until they intersect. It is also desirable that the sidewalks at the corners be level; that is, the points a a in Fig. 38 should all be placed at the same eleva tion, which will make the entire street section, includ ing sidewalks, horizontal across the direction of travel on each street.
On very steep slopes it may not be possible to flatten out the grade to a level in crossing transverse streets, and in such cases the elevations require study, and need to be carefully worked out for each particular case. In
the report of Messrs. Rudolph Hering and Andrew Rosewater upon the streets of Duluth, it is recom mended that in all cases the grade shall be reduced to 3 per cent between the curb lines of cross streets, the grade of the curb reduced in all cases to 8 per cent for the width of the sidewalks of intersecting streets. This is to be considered the maximum allowable rate of transverse grade, and only to be employed in case of necessity. If in Fig. 38 the arrow represents the direc tion of steep slope, and the street transverse to that direction has a roadway 4o feet wide with sidewalks feet wide, the above limits would permit the curb at c to be 1.2 feet lower than that at b, and admit of a fall of o.8 foot in the curb line from a to b and from c to d. If both streets have the same grade and width the curb the lowest corner would be 2.4 feet lower than at the highest corner.
Sometimes, where the parallel streets in one direction follow the lines of greatest slope, and the cross streets are normal to them, the proper grades at intersections may be arranged by giving the streets along the slope a section similar to that shown in Fig. 32 throughout its length, thus permitting the street in the of slope to continue its grade across the intersection without altering at that point the side slope of the cross street.
For a case of maximum slope this would make the section of the roadway of the cross street a plane sur face sloping uniformly from the upper to the lower curb, or in Fig. 35 it would transfer the street crown to the upper curb.