PART II.

CHAPTER IX.

CARRIAGEWAYS AND FOOTWAYS.

PRELIMINARY REMARKS-FOUNDATIONS AND PITCHED PAVEMENTS.

412. The method of paving streets and carriageways, which forms Part II. of this treatise, will now be described, beginning with the earlier kinds of material used, such as cobblestones, and finishing with what is now employed in the large cities and towns of this country.

The historical part of this subject, as also the methods adopted in obtaining many of the kinds of material used for paving purposes, but especially in connection with the construction and repairs of macadamized roads by steam-rolling, have been fully explained in the different chapters in Part I. Such matters, therefore, will only be alluded to in the following pages so far as necessary to further elucidate or amplify the subject.

Stone in many different forms has been made use of as a paving material from the time of the Romans, who employed blocks of an irregular shape laid on a foundation of concrete, which presented great solidity and was extremely durable.

The surface of these large blocks, however, does not afford a good foothold for horses, owing to its wearing smooth; consequently this form of paving is not reliable for modern traffic.

Boulder or cobblestone pavements were much used in the towns of this country until they were superseded by a regular pitched paving. Cobbles make a very noisy pavement, and from the irregular shape of the stones it is impossible to joint them closely, consequently the surface cannot be properly cleansed, therefore boulders form an unsuitable as well as an insanitary paving material. Streets in many of the English towns are still paved with cobbles, but these are being gradually replaced by better descriptions of pavement.

The large regular shaped blocks 8 inches wide which were introduced

in more recent years have been gradually reduced in size, the width of the setts now used being generally 3 inches, laid on a foundation of Portland

cement concrete.

413. The other materials used at the present time for paving carriageways are wood, asphalte, brick, tar-macadam, many kinds of artificial stone and blocks, and ordinary road metalling consolidated by steamrolling.

Where the vehicular traffic is very heavy, and the annual cost of maintenance and scavenging consequently high, it is desirable to apply either of the paving materials already mentioned, so as to provide a harder and more durable surface, and construct a more permanent roadway than can be made by the use of ordinary macadam.

414. In this country, authorities on the subject fix the limit for traffic at 40,000 tons per yard-width of road per anuum, and for maintenance, including cleansing and watering, at a cost of 2s. per square yard annually for macadamized roads. When these figures are reached, that description of pavement should be adopted which is most suitable to the location of the thoroughfare and the class of traffic passing over it. It should be remembered that certain specific interests have to be considered in dealing with this somewhat complicated question.

The principal points in connection with this are the first cost of construction and subsequent maintenance. The description of material selected should not be unduly noisy or dirty, as this would annoy the residents and injuriously affect business premises and shops adjoining the streets. The interest of owners of horses and vehicles, as they are the principal users of the streets, merits a considerable share in the consideration of the subject. Ease of traction, which means the economical conveyance of merchandise, has to be considered, as has also the immunity from accidents by falls, that is, the comparative safety for travelling. Neglect of these considerations and the consequent damage to horses' legs and hoofs, will necessarily represent a considerable loss of money annually, and attention to them a proportionate diminution of loss.

Economy in the ultimate cost for construction and maintenance is of considerable importance, and affects the ratepayers directly, while noiselessness and absence from dust or mud affect pedestrians, business people and shopkeepers, and, on the other hand, good foothold and smoothness affect all those who own horses and vehicles.

415. Some of the essential features which a good pavement for the carriageways of cities and towns should possess, may be summarized as follows:

(1) It should be impervious.

(2) It should be suitable for varying gradients and afford good foothold for horses.

(3) It should be durable, moderate in first cost and subsequent annual repairs, have sufficient curvature to throw off surface water rapidly, and be non-absorbent and easily cleansed.

(4) It should be as noiseless as possible.

(5) It should be constructed with a sufficient foundation for the class of traffic which it has to bear, so as not to subside under the influence of heavy loads.

(6) It should present a uniform and smooth surface, so as to render traction easy.

All the conditions enumerated affect those interested in a varying degree; consequently the usual difficulty is to carry out one or two of the essential requirements mentioned without sacrificing the individual interests of many of the inhabitants.

The details referred to affect the several kinds of pavement differently, and will therefore be described under each separate class.

416. A pavement which is eminently suitable for the thoroughfare of a provincial or agricultural town will not, in the generality of cases, be appropriate for the carriageway of a city or manufacturing town where the streets are subjected to a heavy and continuous traffic. Neither the physical features of a town, nor the climate, should be lost sight of in determining the pavement most suitable for a street or carriageway.

As illustrating the effect of traction on some of the different kinds of materials used, the following table, now universally adopted, may be given previous to describing in detail the construction of the several pavements made use of at present for provincial and metropolitan street traffic.

TABLE XL.

Traction on level roads formed of different materials, asphalte being taken as the standard of excellence.

Another useful table, prepared from experiments made by Mr. Amos on different descriptions of pavement in the city of London, is here given :

417. Boulder or Cobblestone pavements at one time formed the principal paving, and still exist to a considerable extent in some of the cities and provincial towns in England. They afford a fairly good foothold for horses, but the roughness of the surface makes travelling over them very unpleasant.

This paving, which possesses the merit of cheapness, is easily displaced by the action of the traffic and frost, owing to the irregular shape of the stones, and the inevitable large joints, while at the same time a considerable expenditure of tractive energy is required to move loads over them. For the same reasons it is almost impossible to keep the surface in a clean and sanitary condition.

418. It was found that the increasing vehicular traffic in many of the larger towns entailed a greater cost for maintenance each year, while the discomfort and noise of the boulder pavements, the irregularities caused through wear on macadamized roads, and the manufacture of mud and dust in certain seasons of the year, led to the substitution of a more suitable

class of material in the form of 'cubed granite' or 'setts' for making carriageways and streets.

This class of paving was first introduced into London in 1824 by Telford and laid in Hanover Square, although it is recorded that a pitched pavement was constructed in that city in 1762, replacing an old cobblestone pavement. The stones or setts then used were much larger, compared with the practice at the present time, being generally from 6 to 8 inches wide, 9 inches deep, and 12 inches long.

The earlier pavements laid in London and other towns were constructed in the following manner :-After the soil had been removed to a proper depth and the foundation properly prepared, a substratum of metalling or hard core was spread generally to a thickness of from 9 to 12 inches; in streets, however, which had to bear the heaviest traffic the bottoming was increased in thickness to 15 inches. On this stratum was spread a coating of sand into which the setts were bedded. The principal thoroughfares in London at that period (1828 to 1838) were thus laid, the setts being of Aberdeen granite, 6 to 7 inches wide and 9 inches deep.

This class of pavement had a life of from fourteen years in Fleet Street to twenty-four years in Cannon Street; the first cost averaged from 11s. to 17s. per square yard, while the amount expended annually for repairs up to the year 1840 was 12d. in the former street, and 1d. per square yard in the latter thoroughfare. In the year 1854 the annual cost of maintenance had risen to 3d. per square yard in Fleet Street.

These paving setts when lifted were re-dressed and used again in some subsidiary street where the traffic was not heavy, where they had a further life, which in some instances extended to about fourteen years, making a total duration of about thirty years.

In many cases the paving setts were laid directly on the subsoil, after this had been formed to a proper contour, and the joints were filled with sharp sand or fine gravel.

The dimensions of paving setts were reduced about the year 1850 to 5 inches in width, subsequently to 4 inches, and then 3 inches, which width, with a depth of 7 inches and a length not exceeding 12 inches, are, with a few exceptions, the standard sizes of paving setts employed at the present time.

The system of laying the paving direct on the prepared ground and even on a loose stratum of hard core, although still followed in many instances, has been gradually superseded by forming the foundation with Portland cement concrete. The thickness and strength of this class of foundation is regulated according to the amount and class of the traffic which has to be accommodated.

419. The Euston Pavement.'-One of the first really good pitched pavements made in London was that known as the 'Euston Pavement,'