The location, grading and drainage of highways : a concise discussion of general principles illustrated by current and recommended practice ; by Harger Wilson Gardner 1882-

Author:Harger, Wilson Gardner, 1882- [from old catalog]
Language: eng
Format: epub, pdf
Tags: Roads
Publisher: New York [etc.] : McGraw-Hill book company, inc. ;
Published: 1921-03-25T05:00:00+00:00

GRADES AND ALIGNMENT

115

the logical ruling rate. This is based on a load of 5000 pounds for farm hauling which includes wagon weight. The records of produce dealers in the Eastern States show that the ordinary wagon weighs about 1350 lb. and that 3500 lb. is a large net load. This load of 2.4 tons corresponds with the maximum theoretical load for 7 per cent, hard surfaced grade. Team loads of six tons would be very unusual which means that the ideal teaming grade of 23-^ per cent, need not be considered except in level country where it can be obtained without much extra cost.

Effect of Construction Cost on Maximum Grade. —From the standpoint of construction cost 5 to 7 per cent, can generally be built without excessive expenditure even in hilly country.

Maximum Grades in Present Use. —The maximum grades in present use represent the best judgment of engineers from all over the w^orld backed by practical experience and traffic tests of generations. It is true that they are largely based on factors of horse traffic, reasonable construction and maintenance costs but the author beheves that these factors are still the most important deciding elements in the selection of maximum grade for most roads. The following Table 13 gives the rates in common use and is probably the most reliable basis for design that can be used.

Table 13.— Maximum Grades in Foreign Countries

Military highway over the Alps—Italian side, 4,1^ per cent., Swiss side, 6 per cent.

Location

National roads. Departmental per cent. roads, per cent.

Subordinate roads, per cent.

France.

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