HIGHWAY CONSTRUCTION 



or the vertical rise in the same, to F, or the force required to sustain 

 the vehicle on the incline; and A G, or the horizontal distance in 

 which the rise occurs, to P, or the force with which the vehicle presses 

 upon the surface of the road. Therefore, 

 W :AB : :F : G B, 



and 



W :AB : :P : A G. 



If to A G such a value be assigned that the vertical rise of the 

 road is exactly one foot, then 



F . = W sin A 



AB i/AG'+l 



and 



W-AG W AG 

 P = = W cos A, 



AB i/AG a +l 



in which A is the angle BAG. 



To find the force requisite to sustain a vehicle upon an inclined 

 road (the effects of friction being neglected), divide the weight of the 

 vehicle and its load by the inclined length of the road, the vertical 

 rise of which is one foot, and the quotient is the force required. 



To find the pressure of a vehicle against the surface of an inclined 

 road, multiply the w y eight of the loaded vehicle by the horizontal 

 length of the road, and divide the product by the inclined length of 

 the same; the quotient is the pressure required. 



The force with which a vehicle presses upon an inclined road 

 is always less than its actual weight; the difference is so small that, 

 unless the inclination is very steep, it may be taken equal to the 

 weight of the loaded vehicle. 



To find the resistance to traction in passing up or down an 

 incline, ascertain the resistance on a level road having the same surface 

 as the incline, to w T hich add, if the vehicle ascends, or subtract, if 

 it descends, the force requisite to sustain it on the incline; the sum 

 or difference, as the case may be, will express the resistance. 



Tractive Power and Gradients. The necessity for easy 

 grades is dependent upon the pow r er of the horse to overcome the 

 resistance to motion composed of the four forces, friction, collision, 

 gravity, and the resistance of the air. 



All estimates on the tractive power of horses must to a certain 



