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The impracticability of early improvement is generally dictated by economic conditions, but a secondary limiting factor is the shortage of material and labour resources under existing conditions. Where even improvements, which are limited to the existing carriageway and which are necessary to ensure the soundness of a seal coat, cannot be carried out at a reasonable cost, or wherever there is a special case for the adoption of more permanent standards now, then full reconstruction is undertaken. This is then carried out on sound permanent lines to standards which take due regard of traffic, both present and potential, to the end that such major reconstruction shall be lasting and shall be in accordance with the best modern highway engineering practice. With regard to sealing proposals from counties, loan-money is often involved, and generally, whether such or not is the case, counties desire to make one permanent job when they seal. This, of course, has usually involved reconstruction. While a great deal of consideration has been given to the planning of motorways, of necessity looking well to the future, actual work has been confined to those sections immediately adjacent to the major cities where the high traffic volumes and deficiencies of the existing facilities have created justifiable demand. Such work must be of a permanent nature, and construction must therefore be carried out to reasonably high standards. To aid the Board in formulating policy and as a guide to the priority demands of particular highways, it is proposed to conduct a Dominion-wide traffic census during the coming statistical year. The last census was carried out in 1938, and although there has not been normal development during the intervening years, it is now considered that an up-to-date count should not be delayed any longer. In this census more attention will be paid to the tallying of heavy vehicles of various classes. Particular mention may be made of surfacing work which the Board has been developing in the Kotorua-Taupo area. Following on experimental work which was conducted with local materials, the Board has now constructed a considerable mileage of hot-laid bituminous-mix surfacing. Sealing in the pumice country in the centre of the North Island presents some distinct problems. No suitable source of sealing-chips has yet been discovered, and even if chips were available our standard surface-seal methods could not be applied without considerable modification. Although it may be well compacted, pumice falls far short of a properly stabilized metal aggregate or a macadam pavement in unconfined stability and surface hardness. However, it is free draining, non-plastic, and little effected by varying normal moisture conditions, so that it has good foundation properties. Thus, providing it is properly prepared and is contained and protected by a suitable surface coating, it is satisfactory for building up the pavement strength. Good-quality pumice should be used, and it should be placed in layers and thoroughly compacted under moist conditions to the required depth. Pumice must have some additional strength of surface coating over what would be required on a normal metal surface. In the first place, our standard seal of one coating of chips would be unsatisfactory, because the pumice has insufficient strength to resist the large chip being punched into it. This would quickly cause disruption and break-up of the seal coat. Secondly, there is little bond between the bituminous carpet and the pumice surface, so that there is a lack of horizontal shear strength along the plane of junction of the pumice and surface pavement. There is not the strong keying action provided by the texture of a crushed stone surface. Any bituminous surfacing laid direct on pumice must therefore be of a nature which will not be pushed into the pumice. Also, it must be constructed thickly enough to withstand the shearing force of traffic, and to sufficiently reinforce and protect the pumice base. Two-coat chip sealing, using tar and a large chip followed by road oil and a smaller chip, was formerly used to carry out some surfacing work in the area. Metal chips had to be imported long distances, however, and the work was costly. Under fight pre-war loadings this treatment lasted well, but where loadings have become more severe much of it has failed and heavy reseal coats have been necessary.

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