KIND OF PAVEMENT Pounds per too In terms of the toad Asphalt (sheet) 30 to 70 A. to t 'l Bruck 15 •• 40 t 1 - as Cobblestones 50 •' 100 1 1 TT Stone-block 30 •• 84 1 • 1 lS Wood-block rectangular 30 •• • 1 afi Wood-block round 40 ^ 3 S Serviceability. The serviceability of a pavement is its quality of fitness for use. This quality is measured by the expense caused to the traffic using it—namely, the wear and tear of horses and vehicles, loss of time, etc. No statistics are available from which to deduce the actual cost of wear and tear.
The serviceability of any pavement depends in great measure upon the amount of foothold afforded by it to the horses—provided, however, that its surface be not so rough as to absorb too large a per centage of the tractive energy required to move a given load over it. Cobblestones afford excellent foothold, and for this reason are largely employed by horse-car companies for paving between the rails; but the resistance of their surface to motion requires the expenditure of about 40 pounds of tractive energy to move a load of 1 ton. Asphalt affords the least foothold; but the tractive force required to overcome the resistance it offers to motion is only about 30 pounds per ton.
Comparative Safety. The comparison of pavements in respect of safety, is the average distance traveled before a horse falls. The materials affording the best foothold for horses are as follows, stated in the order of their merit: (1) Earths, dry and compact.
(2) Gravel.
(3) Broken stone (macadam).
(4) Wood.
(5) Sandstone and brick.
(0) Asphalt.
(7) Granite blocks.
Durability. The durability of pavement is that quality which determines the length of time during which it is serviceable, and does not relate to the length of time it has been down. The only measure of durability of a pavement is the amount of traffic tonnage it will bear before it becomes so worn that the cost of replacing it is less than the expense incurred by its use_ As a pavement is a construction, it necessarily follows that there is a vast difference between the durability of the pavement and the durability of the materials of which it is made. Iron is eminently
durable; but, as a paving material, it is a failure.
Durability and Dirt. The durability of a paving material will vary considerably with the condition of cleanliness observed. One inch of overlying dirt will most effectually protect the pavement from abrasion, and indefinitely prolong its life. But the dirt is expensive, it injures apparel and merchandise, and is the cause of sickness and discomfort. In the comparison of different pavements, no traffic should be credited to the dirty one.
Life of Pavements. The life or durability of different pavements under like conditions of traffic and maintenance, may be taken as follows: Cost. The question of' cost is the one which usually interests taxpayers, and is probably the greatest stumbling-block in the attain ment of good roadways. The first cost is usually charged against the property abutting on the highway to be improved. The result is that the average property owner is always anxious for a pavement that costs little, because he must pay for it, not caring for the fact that cheap pavements soon wear out and become a source of endless annoyance and expense. Thus false ideas of economy always have stood, and undoubtedly to some extent always will stand, in the way of realizing that the best is the cheapest.
The pavement which has cost the most is not always the best; nor is that which cost the least the cheapest; the one which is truly the cheap est is the one which makes the most profitable returns in proportion to the amount expended upon it. No doubt there is a limit of cost to go be yond which would produce no practical benefit; but it will always be found more economical to spend enough to secure the best results, and this will always cost less in the long run. One dollar well spent is many times more effective than one-half the amount injudiciously expended in the hopeless effort to reach sufficiently good results. The cheaper work may look as well as the more expensive for the time, but may very soon have to be done over again.