Selecting the Pavement

SELECTING THE PAVEMENT The problem of selecting the best pavement for any particular case is a local one, not only for each city, but also for each of the various parts into which the city is imperceptibly divided; and it involves so many elements that the nicest balancing of the relative values for each kind of pavement is required, to arrive at a correct conclusion.

In some localities, the proximity of one or more paving materials determines the character of the pavement; while in other cases a careful investigation may be required in order to select the most suitable material. Local conditions should always be considered; hence it is not possible to lay down any fixed rule as to what material makes the best pavement.

The qualities essential to a good pavement may be stated as follows: (1) It should be impervious.

(2) It should afford good foothold for horses.

(3) It should be hard and durable, so as to resist wear and dis integration.

(4) It should be adapted to every grade.

(5) It should suit every class of traffic.

(6) It should offer the minimum resistance to traction.

(7) It should be noiseless.

(8) It should yield neither dust nor mud.

(9) It should be easily cleaned.

(10) It should be cheap.

Interests Affected in Selection.

Of the above requirements numbers 2, 4, 5, and (i affect the traffic and determine the cost of age by the limitations of loads, speed, and wear and tear of horses and hicles. If the surface is rough or the foothold bad, the weight of the load a horse can draw is decreased, thus cessitating the making of more trips or the employment of more horses and vehicles to move a given weight. A defective surface necessitates a tion in the speed of movement and consequent loss of time; it increases the wear of horses, thus decreasing their life service and lessening the value of their current services; it also increases the cost of maintaining vehicles and harness.

Numbers 7, 8, and 9 affect the occupiers of adjacent premises, who suffer from the effect of dust and noise; they also affect the owners of said premises, whose income from rents is diminished where these disad vantages exist. Numbers 3 and 10 af fect the taxpayers alone—first, as to the length of time during which the covering remains serviceable; and sec ond, as to the amount of the annual repairs. Number 1 affects the adjacent occupiers principally on

hygienic grounds. Numbers 7 and 8 affect both traffic and occupiers.

Problem Involved in Selection. The

problem involved in the selection of the most suitable pavement consists of the following factors: (1) adaptability; (2) desirability; (3) serviceability; (4) dura bility; (5) cost.

Adaptability. The best pavement for any given roadway will depend altogether on local circumstances. Pavements must be adapt ed to the class of traffic that will use them. The pavement suitable for a road through an agricultural district will not be suitable for the streets of a manufacturing center; nor will the covering suitable for heavy traffic be suitable for a pleasure drive or for a residential district.

General experience indicates the relative fitness of the several materials as follows: For country roads, suburban streets, and pleasure drives—broken stone. For streets having heavy and constant traffic—rectangular blocks of stone, laid on a concrete foundation, with the joints filled with bituminous or Portland cement grout. For streets devoted to retail trade, and where comparative noiselessness is essential—asphalt, wood, or brick.

Desirability. The desirability of a pavement is its possession of qualities which make it satisfactory to the people using and seeing it. Between two pavements alike in cost and durability, people will have preferences arising from the condition of their health, presonal pre judices, and various other intangible influences, causing them to select one rather than the other in their respective streets. Such selections are often made against the demonstrated economies of the case, and usually in ignorance of them. Whenever one kind of pavement is more economical and satisfactory to use than is any other, there should not be any difference of opinion about securing it, either as a new pavement or in the replacement of an old one.

The economic desirability of pavements is governed by the ease of movement over them, and is measured by the number of horses or pounds of tractive force required to move a given weight—usually one ton—over them. The resistance offered to traction by different pave ments is shown in the following table: Resistance to Traction on Different Pavements