CONSTRUCTION OF ROADS.

Taranaki Daily News, 1 June 1920, Page 4

CONSTRUCTION OF ROADS.

VVKLLIXCiTON ENGINEER'S SERVATIONSGREAT STAT!-: HIGHWAYS. In the course of a voluminous report to the Wellington City Council, the city engineer (Mr. W. H. Morton) gives a mass of valuable information on matters of concern, to municipalities, gleaned during his recent visit to Canada, the United States, United Kingdom, and the Continent. Chief among the problems every local body is faced with is road construction in relation to modern forms of traffic. Mr. Morton deals with this subject interestingly as follows: "I had not been long in America when I was forced to the conclusion that one of the. principal matters for consideration and investigation wag the method of road construction, more particularly in the cities. In practically the whole of the cities of America wood blocks, granite setts, and bricks are to be found in use for street paving, but for general city work the use of bituminous asphalt predominates in business thoroughfares, and in the best residential streets. At the approaches to wharves and railway stations which are subject to heavy and slow-moying traffic granite setts or wood blocks are mostly used for street pavements.

The wood pavements are generally of blocks laid on a principle somewhat similar to the wood pavements of this city, but the timber used is that known in Australasia as oregon pine, but throughout America as Douglas fir. In America, however, the wood pavements did not appear to be very satisfactory', innumerable instances of irregularities and depressions being found. Without doubt the pavement which finds most favor for street work is sheet asphalt and bituminous concrete, which later is varied somewhat in different places, and variously known as bitlmlithic, To'peka mix, and Warrenite. When referring to this material afterwards the term bituminous cowapte will be used as such more clearly indicates the nature of the material.

'One of the principal thoroughfares of New York City, Fifth Avenue, is paved with sheet asphalt, and, notwithstanding the heavy and fast-moving traffic (including motor buses in great numbers),, this' material appeared to great advantage, being quite sanitary and not slippery It was distinctly noticeable how few horses were en ,r a ir eu m cartage of any description, more" particularly in the Western States. I was informed on good authority that in California there is one motor vehicle to every seven of the population, and that it does not take one long to believe that the statement is absolutely correct. Horses were scarcely ever to be seen excepting only in the vicinity of dockyards. .The result is that, "so far as road surfaces are concerned, horse traffic has been eliminated from consideration. This simplifies to a very great extent the difficulties to be orercome as compared with those met with in a eitv where the traffic is in a transition stage, and where consideration has to be given to fast-moving motor vehicles, which cause considerable damage to waterbound macadam road surfaces, and where at the same time there must be, a surface which wffl not be so slip, pery as to prevent horses getting'a grip of it. STATE HIGHWAYS. "The State highways constructed by the counties in the various States are in many instances of a wonderful character. For instance, in Portland, Oregon, I was driven over the Columbia River Highway. This extends for fifty miles from the town of Portland to the Columbia River, and then along the banks of this magnificent river for many miles. This highway, however, seemed to be used principally for pleasure purposes, there being at the time of my visit scarcely any traffic other than ordinary touring automobiles. The paviijg is of Warrenite or bituminous concrete, about 24 feet in width, and with a surface particularly even and satisfactory for motor traffic. The money spent upon its construction was considerable (about £275,000). There

are very many expensive structures of concrete in retaining walls and bridges, designed to enable the road to be carried past ravines and over streams, and which are extremely interesting. CONCRETE ROADS. "In many parts of California as well as in Wayne County, qear Detroit and elsewhere, great use has been made of concrete for road construction- The concrete invariably is not reinforced. After travelling ( over hundreds of miles of such roads, the conclusion was forced upon one that they were eminently suitable ■for motor traffic provided that the foundation on which they were constructed was absolutely firm and rigid. In only one place, outside of Los Angeles, was my attention drawn to a defective piece of road made of this material, and the defect was clearly due to the unsatisfactory nature of the sub.-foiuidation. The width of the concrete roadways varied from 12 to 20 feet. It was not considered necessary to increase the width beyond 20ft., since a third line of vehicles could not be accommodated unless the width were made at least 28 feet, and from observations made there could be no doubt that, for highways*, room for two vehicles to pass comfortably is all that is necessary, aud 20 feet easily meets this requirement. The material in the concrete roads requires to be of the best description. A rich mixture is used, and great care is taken to prevent any voids occurring. One coat work is now generally accepted as being most satisfactory- The depth varies according to local conditions, and may on the average be put down as 7A inches, although in some instances a depth of eight or nine inches has been provided. The surface is generally finished off with long-handled rollers rolling from one side of the road to the other, and bv means of a belt drawn across the surface. Although provision for expansion is made on nearly all such roadways many cracks are visible. These are Invariably due to temperature stresses. No notice is taken of them, and they are remedied by pouring in bitumen when at their greatest width in order to prevent, deterioration of the concrete at the edges. GRANTTE SETT PAVEMENTS. "Granite sett pavements are to be fcund on the approaches to all wharves, railway, and goods stations, and, so far as tasting qualities are concerned, give a -better result than any other class of material. They are, however, not so sanitary and do not form an ideal surface for present-day traffic. BRICK PAVEMENTS. '•"Brick pavements were in many cities uneven in character and unsatisfactory. These were, however, originally laid over a concrete foundation on a sand cushion.

A recent, practice lias been to lay the bricks directly on the concrete bedding and grouting them in with cement mortar, in such a way that they become part of a homogeneous mass, comprising both bride and concrete. This method, which I saw particularly in Seattle, appeared to be highly satisfactory. The roads had not been subjected to great tests, but. there appeared to be no doubt that they would satisfactorily withstand motor car traffic of all'descriptions. The bricks were of a special character, burnt very hard, and specially made for this class of work. WOOD PAVEMENTS. "The wood pavements are similar in almost every respect to those laid in this and other countries. special mention, therefore, requires to he made except to say that in my opinion the use of soft wood, whether creosoted or untreated for street paving purposes, is not satisfactory as the use of hard: woods, when subject to heavy traffic and if properly laid. They are subject to the same difficulties which arise from expansion and contraction, and which constitute one of the greatest troubles in dealing with pavements of this description.

WATER-BOUND MACADAMISED ROADS. 'fin scarcely any of' thte American cities visited were any water-bound macadamised roads to' be observed, which were better than similar roads constructed in cities of New Zealand- As a matter of fact where the roads surfaces had not been paved with permanent material, such as street asphalt, bituminous concrete, woodblocks, bricks or granite setts, the roads were in very bad condition indeed, most of them having an earth surface. Where such was the case kerbing, guttering, and footways were in an equally bad condition, many of the streets having for a footway simply a few planks' fastened together and laid in much the same way as the duckwalks used in the trenches during the recent wav. On making inquiries as to how such a state of affairs existed, wherein some streets were paved with the most expensive and permanent materials, and' others were left in a deplorable condition, it was at once ascertained that the method of financing permanent pavement construction was the sole reason.