HIGHWAY CONSTRUCTION 



75 



that the rectangle AAAA shall appear to l>e nearly level; but to secure 

 this it must actually have a considerable dip in the direction of the 

 slope of the street. If steep grades are continued across intersections, 

 they introduce side slopes in the streets thus crossed, which are trouble- 

 some, if not dangerous, to vehicles turning the corners, especially the 

 upper ones. Such intersections are especially objectionable in rainy 



300 



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Fig. 48. 



weather. The storm water will fall to the lowest point, concentrating 

 a large quantity of water at two receiving basins, which, with a broken 

 grade, could be divided between four or more basins. 



Fig. 48 shows the arrangement of intersections in steep grades 

 adapted for the streets of Duluth, Minn. From this it will be seen 

 that at these intersections the grades are flattened to three per cent for 

 the width of the roadway of the intersecting streets, and that the grade 

 of the curbs is flattened to eight j>er cent for the width of the intersecting 

 sidewalks. Grades of less amount on roadway or sidewalk are con- 

 tinuous. The elevation of block-corners is found by adding together 

 the curb elevations at the faces of the block-corners, and 2J per cent of 



