MODERN TRAFFIC ROADS.

Manawatu Herald, Volume XLI, Issue 1926, 14 January 1919, Page 1

MODERN TRAFFIC ROADS.

COMPARISON OP COST. A comparison of: different methods of road construction, based on actual figures quoted by New Zealand engineers, is given by Air J. P. Holloway in an article on the Utility of Tarred Roads. The cost of tar sealing is estimated at 8s per square yard for one eoat. A second coat should be applied at a cost of fid per square yard, making a total cost of Is 2d, or £5 'ls 3d per mile of 15 ft. road. This class of treatment, he states, should be applied only to existing roads of substantial construction. Tar scaling should not lie attempted on a weak or poorlyformed road. No surface treatment will make a poor road good, but will keep a good road from going in places, and the wearing surface will be cheaper to maintain, whilst the cost of renewing is entirely eliminated. Tar grouting is extensively adopted by New Zealand and American engineers where it is desired to construct a new road. The result is a smooth, resilient wearing surface, -with a tar concrete foundation. The cost ol (his class of road in New Zealand works out at £1,308 13s per. mile of 15ft. road. The above figures are for the construction of an entirely new road, capable of carrying the heaviest form of mixed tralfic. Tar concrete for city traffic works out at £1,570 per mile of 15 feet road, or 3s 7d per square yard. For the purpose of comparison the writer puts down the cost of a cement concrete; road, suitable for country traffic, at £4,705 per mile (or 10s 8d per square yard), and to (his must be added the cost of a wearing surface blanket at approximately 8d per square yard. On the question of maintenance the writer states that the view of most engineers is that the wearing surface alone must be taken into account. A permanent road, such as cement concrete, tar concrete, or tar grout, should be in position for all time, provided the wearing surface is kept intact. Thus beyond the annual interest and sinking fund charges maintenance really amounts to the cost of preserving the wearing surface, which in each case should lie the same. The cost of maintenance according to the report of one engineer in charge of 70 miles of tarred roads, is 15s per chain per annum. In computing maintenance, the most important item to lake into account is (he renewal of a metalled road at end of its life (5 to 7 years). There is a considerable amount of controversy as to how long a cement concrete surface will stand up to mixed traffic before a covering is required. New Zealand experience so far has proved that twelve to eighteen months is long enough, whilst American experience says five years. The writer quotes figures to show that the annual cost of maintenance, covering, a period of twelve years, is as follows: Tar macadam £154 per mile, cement concrete £340, and gravelled roads £3,1(). Constantly deteriorating metal roads have had their day, .-ays Mr Holloway. Modern traffic conditions require roads in keeping and raw metal highways are a waste of money.