ROADS 171 



and weigh from 3 to 6 tons. To overcome the difficulty of 

 turning the roller about, a tongue with a wheel truck is 

 attached to a yoke which is pivoted directly over the center 

 of the roller drum, and which may be unlatched from one 

 side and turned about to the opposite side and latched, 

 enabling the drum to be drawn in the reverse direction with- 

 out turning. Rollers made of cast-iron cost about $100 per 

 ton of weight. Cheaper rollers are made by building up 

 the hollow drum of cast iron or steel plate, and filling with 

 water or concrete. In the construction of stone roads it is 

 highly essential that a heavy roller be used, and for this 

 reason the horse roller is seldom used. 



Power Rollers. The steam roller is of two types one 

 known as the three-wheel roller and the other as the tandem 

 roller. The three-wheel roller resembles the traction engine, 

 in which the guide wheels are replaced with a rolling drum 

 and the drivewheels have smooth treads. Gasoline and oil 

 engines are being substituted for steam power for rollers 

 to some extent. Many traction engines are made so as to be 

 easily equipped in this way. The weight of these rollers 

 varies from 10 to 20 tons and the pressure under the drivers 

 will vary from 450 to 650 pounds per inch of width. 



Tandem rollers, sometimes called asphalt rollers, con- 

 sist of two rolling drums at the ends of a frame. Most of the 

 weight is applied to one of these drums, which is driven by 

 power from a steam or a gasoline engine, and the other is 

 used for guiding. This type of roller tends to leave the sur- 

 face smoother than the three-wheel type, but cannot be 

 handled quite as conveniently over country roads. Although 

 it can be used for drawing other machines it is not used so 

 extensively in this connection as the three-wheel type. It 

 cannot be provided with spikes for loosening old road sur- 

 faces preparatory to resurfacing. 



