HIGHWAY CONSTRUCTION 



PART I. 



COUNTRY ROADS. 



GENERAL CONSIDERATIONS. 



Object of Roads. The object of a road is to provide a way 

 for the transportation of persons and goods from one place to another 

 with the least expenditure of power and expense. The facility with 

 which this traffic or transportation may be conducted over any given 

 road depends upon the resistance offered to the movement of vehicles. 

 This resistance is composed of: (1) The resistance offered by the 

 roadway, which consists of (a) "friction" between the surface of 

 the road and the wheel tires; (b) resistance offered to the rolling of 

 the wheels, occasioned by the want of uniformity in the road surface, 

 or lack of strength to resist the penetrating efforts of loaded wheels, 

 thus requiring the load to be lifted over projecting points and out of 

 hollows and ruts, thereby diminishing the effective load the horse 

 may draw to such as it can lift. This resistance is called "resistance 

 to rolling" or "penetration;" (c) resistance due to gravity called 

 "grade resistance;" (2) The resistance offered by vehicles, termed 

 "axle friction;" (3) Resistance of the air. 



The road which offers the least resistance to traffic should com- 

 bine a surface on which the friction of the wheels is reduced to the 

 least possible amount, while offering a good foothold for horses, to 

 enable them to exert their utmost tractive power, and should be so 

 located as to give the most direct route with the least gradients. 



Friction. The resistance of friction arises from the rubbing of 

 the wheel tires against the surface of the road. This resistance to 

 traction is variable, and can be determined only by experiment. 

 From many experiments the following deductions are drawn : 



(1) The resistance to traction is directly proportional to the 

 pressure. 



