If the use of motor vehicles equipped with pueumatic tires be comes general, it is possible that some other description of binding material will be necessary. The pumping action of suction created by pneumatic tires, especially when propelled at a high speed, causes a considerable movement of the fine particles of the binding material, which on being displaced will convert the covering into a mass of stones. This objection can probably be overcome by watering.
Compacting the Broken Stone. Three methods of compacting the broken stone are practiced : (1) by the traffic passing over the road; (2) by rollers drawn by horses; (3) by rollers propelled by steam. • The first method is both defective and objectionable. (1) It is destructive to the horses and vehicles using the road. (2) It is waste ful of material; about one-third of the stone is worn away in the oper ation. (3) Dung and dust are ground up with the stone, and the road is more readily affected by wet and frost.
Steamrollers were first successfully introduced in France in 1S60, since which time they have been almost universally adopted on account of the superiority and economy of the work done. Their use shortens
the time required for construction or repair, and effects an indirect saving by the reduced wear and tear of horses and vehicles. They are made in different weights ranging from 3 to 30 tons. For the compact ing of broken stone roads the weights in favor are from ten to fifteen tons; the heavier weights are considered unwieldy and their use is liable to cause damage to the underground structures that may be in the roadway.
The advantage of steam rolling may be summed up as follows: (1) They shorten the time of construction.
(2) A saving of road material, (a) because there are no loose stones to be kicked about and worn; (b) because there is no abrasion of the stone, only one surface of the stone being exposed to wear; (c) because a thinner coating of stone can be employed; (d) because no ruts can be formed in which water can lie to rot the stone.
(3) Steam-rolled roads are easier to travel on account of their even surface and superior hardness and they have a better appearance.
(4) The roads can be repaired at any season of the year.
(5) Saving both in materials and manual labor.