HIGHWAY CONSTRUCTION 



extent be vague, owing to the different si mirths ;md speeds of ;miin;ds 

 of the same kind, as well as to the extent of their tmining to ;mv 

 particular kind of work. 



The draught or pull which a good average horse, weighing 1,200 

 pounds, can exert on a level, smooth road at a speed of 2', miles per 

 hour is 100 pounds, equivalent to 22,000 foot-pounds per minute, 

 or 13,200,000 foot-pounds per day of 10 hours. 



The tractive power diminishes as the speed increases and, per- 

 haps, within certain limits, say from J to 4 miles per hour, nearly 

 in inverse proportion to it. Thus the Average tractive force of a 

 horse, on a level, and actually pulling for 10 hours, may be assumed 

 approximately as follows: 



TABLE 3. 

 Tractive Power of Horses at Different Velocities. 



Tractive 

 Force. Lb. 



Ill .11 



100 

 90.91 

 S3 . 33 

 71.43 

 62.50 



The work done by a horse is greatest when the velocity with 

 which he moves is J of the greatest velocity with which he can move 

 when unloaded; and the force thus exerted is 0.45 of the utmost 

 force that he can exert at a dead pull. 



The traction power of a horse may be increased in about the 

 same proportion as the time is diminished, so that when working 

 from 5 to 10 hours, on a level, it will be about as shown in the following 



table: 



TABLE 4. 



Hours per day Traction (pounds) Hours per day Traction (pounds) 



10 100 7 



9 111$ 6 



8 125 5 



The tractive power of teams is about as follows 



1 horse =1 



2 horses 0.95 X 2 =1.90 



3 " 0.85X3 = 2.55 



4 " 0.80X4 = 3.20 



146? 

 166J 

 200 



