10 



HIGHWAY CONSTRUCTION 



important element in any case which arises for settlement. Disre- 

 garding time, the horizontal length of a road may be increased to 

 avoid a 5 per cent grade, seventy times the height. 



Table 7 shows, for most practical purposes, the force required 

 to draw loaded vehicles over inclined roads. The first column ex- 

 presses the rate of inclination; the second, the pressure on the plane 

 in pounds per ton; the third, the tendency down the plane (or force 

 required to overcome the effect of gravity) in pounds per ton; the 

 fourth, the force required to haul one ton up the incline; the fifth, the 

 length of level road which would be equivalent to a mile in length of 

 the inclined road that is, the length which would require the same 

 motive power to be expended in drawing the load over it, as would 

 be necessary to draw over a mile of the inclined road; the sixth, the 

 maximum load which an average horse weighing 1,200 pounds can 

 draw over such inclines, the friction of the surface being taken at 

 -fc of the load drawn. 



TABLE 7. 



* Near enough for practice; actually 2239.888. 



Pressure on the plane = weight x nat cos of angle of plane. 



Axle Friction. The resistance of the hub to turning on the., 

 axle is the same as that of a journal revolving in its bearing, and has 



