ROAD ECONOMICS.

Hauraki Plains Gazette, Volume XXXVI, Issue 4856, 22 July 1925, Page 3

ROAD ECONOMICS.

TYPICAL INVESTIGATION. SYSTEM OF WORKING. The following circular hap been received by all local bodies from the chairman of the Main Highways Board through the District Councils : “The Main Highways Board recently passed a resolution requiring that important proposals for highway improvement (when being submitted by local authorities) should be accompanied by financial statements proving that the. work will be an economical proposition for the ratepayers..

“To enable local authorities to understand the nature of the statement required I append hereto an imaginary investigation. The board has also decided that if local authorities require advice and assistance in this direction the services of the boards’ engineer, Mr A. Tyndall, are to be made available. "Road improvements may) be divided broadly into two classes: (1) Improvements in grade and alignment; (2) improvements in. the running surface.

“When the financial side of any proposal is being investigated, the class into which the improvement comes decides the b.ajsis of finance. Long period loans, yvith small sinking fund, are satisfactory for the first type of improvement. For the second type, however, the improvements are not nearly so permanent, and consequently arrangements should be made for any capital expediture on such improvements to be amortised during the period which may be considered the minimum sure life of the improvements. The extent of improvement warranted under either class is clearly dependent on the traffic. For any particular traffic density the extent of economic improvement is that which may be paid for with the savings in operating cost accruing from the improvement. This investigation will be limited to an improvement of the second type.

"Let us assume the following facts : A water-bound macadam road in poor condition, five miles in length, is costing at the present time £l5O per mile per annum. The average daily traffic throughout the year is 100 motorcars, 30 motor lorries, and 12 motor cycles. It is desired to ascertain the maximum capital expenditure that is warranted in improving the road to a satisfactory standard. . If the average motor-car is l transferred from a water-bound macadam road in poor condition to a good bituminised surface the maximum saving in operating costs that can be expected is %d per mile. In the case of the average mootr truck the maximum saving would probably be about 3d per mile. In. the United States of America the estimated figures are much lower per mile than the above, but the cost ot running motor vehicles in this country its much greater than in the United States, and the savings are therefore proportionately greater. A motor cycle may be assumed as saving per mile. The maximum possible savings, per mile per day on the road under consideration when improved with some form of well constructed bituminous surfacing will be as follows : 100 cars at %<l, ,75d; 30 Ibrries at 3(d, 90d; 12 motor cycles at %d, 3d ; total, 14s a day, or £255 10s per annum.

“Sundays are Included as the motorcar traffic is very often heavier on Sundays than any other day. Tne period over which this investigaaoii will be made is< 10 years, as this is likely to be the life of the form of pavement warranted. It is, therefore, necessary to consider .what the tiaffic is likely to be in five years’ tinie, so that the average annual saving over the whole ten years can be estimated.

“In .the United States, in the absence of extreme conditions, the assumption usually made is that the traffic will be doubled in five years, and this, assumlption is a fair one to make in New Zealand. Therefore, in the next ten years, by improving the road surface, the possible average annual, saving through traffic economies will be double the present day savings ; that, is, £5ll per mile per annum. The present cost of maintenance is £l5O a mile. If an attempt were made to maintain the existing road under the increased traffic it quite likely tiiat the maintenance would increase to £3OO a mild ® ve years’ time. The maintenance on’ the new, form of pavement in five years’ time will be, say, £l2O a mile, so that it is fair to assume that the improved pawement will mean a saving in maintenance expenditure of £lBO per mile per annum. The total possible saving will therefore be £691 per mile per annum. Owing to the fact that estimates of the cost of construction work arc very often exceeded, and owing to other doubtful factors, it is most desirable this estimate of possible savings be a conservative one. The annual overhead charges on the capital expediture should therefore not exceed two-thirds, of tlie anticipated savings. Two-thirds of £691 is £460 13s 4d. “The amount of loan which could be redeemed in ten years at 6 per cent, with an annuity of £4'6o 13s 4d is approximately £34o(k This sum 16presents the maximum capital expenditure per mile that is warranted in (surface improvemenfis on the road in , question under the traffic intensity specified. "It will be observed under these assumptions that for the first five years the community will really be losing money on the proposition, as the traffic will not have increased (sufficiently to bring the savings hr operating costs. up to the estimated average amount. If an immediate return is required on the capital expenditure the cost of. the improvements would have to be limited to one-half of the above figures, i.e., £l7OO per mile per annum. Any proposition which would provide a good running surface at an expenditure of any amount from £l7OO to £3400 per mile would be economically sound. “Investigations made on tihe lines of the above should always incline

towards the conservative side, for. the following reasons: (1) Estimates of the cost of construction work are very often exceeded; (2) the traffic may or may not increase 400 per cent, in the next ten yeans. In a number of localities progress and increase in population are below the normal, and consequently it may'be predicted that the motor traffic in such localities will not increase to the extent that it will in other parts of tire country. (3) The anticipated savings in transfer- ' ring the traffic from one type of pavement to an improved type will not always reach the figure assumed in the above calculations, e.g., the savings in operating costs to be derived by transferring a motor-car from a tar-sealed road in fair condition to a concrete road would probably not be more than %d per mile.

“Similarly, the operating costs on a gravel road in good condition are very little more than the opeiatiiit, costs on a bituminous surface. It is said by a competent American authority that possibly only 3 per cent, to 5 per cent, of the operating cost is saved by raising the standard of pavement construction beyond that of a well maintained water-bound macadam road. “In conclusion, the Mains Highways Board fully realises that road economics is anything but an exact science ; but it feel's that if an hon est enedavour is made to apply the general principles outlined above to further highway schemes sound decisions will result.”