EARTH , SAND-CLAY, AND GEAVEL ROADS. 
13 
5. Table 3, of loads is based on the foregoing statements, assum- 
ing the weight of the average horse at 1,200 pounds, the pull he 
is capable of exerting continuously for several consecutive hours 
on a level road at one-tenth of his weight, his maximum pull on a 
level road, over a distance not to exceed 500 feet without a rest, at 
twenty-five one-hundred ths of his weight; and assuming that a pro- 
portionate part of a horse's energy is devoted to lifting his own 
weight on grades. 
Table 3. — Effect of grades on the gross load a 1,200-pound horse can haul. 1 
Per cent of grade. 
Road through 
deep sand. 
Road over 
average 
dry earth. 
Road over 
firm earth 
or sand-clay. 
Average 
gravel road. 
First-class 
gravel or 
macadam road. 
Contin- 
uous 
load. 
Maxi- 
mum 
load. 
Contin- 
uous 
load. 
Maxi- 
mum 
load. 
Contin- 
uous 
load. 
Maxi- 
mum 
load. 
Contin- 
uous 
load. 
Maxi- 
mum 
load. 
Contin- 
uous 
load. 
Maxi- 
mum 
load. 

Pounds. 
760 
645 
540 
445 
365 
290 
160 
Pounds. 
1,905 
1,720 
1,550 
1,410 
1,275 
1,155 
950 
700 
390 
Pounds. 
1,600 
1,270 
1,010 
800 
625 
480 
250 
Pounds. 
4,000 
3.390 
2,905 
2,515 
2,190 
1,920 
1,490 
1,030 
535 
Pounds. 
2,285 
1,725 
1,325 
1,020 
780 
585 
295 
Pounds. 
5,715 
4,610 
3,805 
3,200 
2,725 
2,340 
1,765 
1,180 
590 
Pounds. 
3,000 
2,160 
1.600 
1.200 
900 
665 
330 
Pounds. 
7,500 
5,760 
4,600 
3,770 
3,150 
2,665 
1,965 
1,285 
630 
Pounds. 
4,365 
2,880 
2,020 
1,460 
1,065 
775 
370 
Pounds. 
10,910 
7,680 
5,810 
4,590 
3 735 
1 
2 
4 
5 
3 100 
7 
2' 215 
10 
l'410 
15... 
675 
1 This table is based upon the assumption that for the same road surface the pull varies 
directly with the weight of the load. Tests to be made may make it necessary to modify 
this assumption. 
Table 3 shows conclusively that for economy the maximum grade 
for any particular road should be fixed with due regard for the type 
of surface to be employed. For example, where the road is through 
deep sand, a horse of the character assumed, by extraordinary exer- 
tion, could pull his allowable continuous load of 760 pounds for level 
grades up a short grade of about 10 per cent, while in the case of a 
firm earth or sand-clay road the allowable continuous load for level 
grades is 2,285 pounds, and the steepest grade up which the horse 
could possibly pull this load is about 5 per cent. For average gravel 
roads the corresponding comparison would show a maximum grade 
of about 4 per cent. 
Comparisons of the kind made in the preceding paragraph are not 
sufficient, of course, to determine the maximum allowable grades for 
any particular road, because, in general, the judgment should be 
largely influenced, in fixing the maximum grade, by the topography 
of the region which the road traverses. According to the best current 
practice, where the road is or is expected to become of sufficient im- 
portance to warrant a highly improved surface, the maximum grade 
usually is fixed with reference to this feature about as follows : 
Per cent. 
Coastal plain and prairie regions 2 to 3 
Average rolling country 4 to 6 
Hilly or mountainous regions 6 to 8 
