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The " Best " Road. Wherever important road-improvements aro being considered there will always be a persistent search for a universally supreme type of road. Conferences of engineers will be continually asked to decide the question, experts from other countries or States will be consulted to enable a decision to be made, and many fruitless arguments will eventuate, particularly between sales engineers of rival organizations. Nevertheless there is no universally best road, any more than there is a best size for boots. When the Federal Aid Road Aot first came into force in America in 1916 the only specification supplied was that the road work carried out with Federal assistance should be " substantial in character." The interpretation of this expression was left to the Secretary of Agriculture, who decided that it was impossible to apply fixed and definite standards because none could bo found which would meet the variety of conditions found throughout the country. Each scheme, accordingly had to bo considered on its own merits. To enable a decision to bo arrived at, the following matters were investigated : — (1.) The amount and nature of traffic using the road at the time of the application as determined by a traffic census : (2.) The probable amount and nature of the traffic which would use the road after improvement : (3.) The type of adjacent roads : (4.) Tho relation of tho road to the State highway system : (5.) The technical questions brought about by local conditions. With thoroughly reliable information on the above points no particular difficulty was encountered in making a fair decision as to the " best " type of road for any particular location. For any particular traffic intensity the economic type is that which can be paid for with the savings in operating costs accruing from the improvement. No road should, be improved to an extent in excess of its earning-capacity, but all roads should be developed to the highest degree consistent with the return in the form of traffic economies. Guided by these considerations all types of roads, from the unsurfaced graded earth roads to concrete, have been approved by the Bureau of Public Roads. Of the total mileage completed or under construction up to the 30th June, 1922, gravel, sand-clay, and earth roads comprised about 70 per cent., water-bound macadam and bituminous macadam about 10 per cent., and. concrete, brick, and bituminous concrete about 20 per Cent. Of this 20 per cent, the mileage of bituminous concrete formed under 3 per cent. The percentage of the money expended on the three main groups was as follows: — Gravel, sand-clay, and earth, 41 per cent. ; watcrbound macadam and bituminous macadam, 14 per cent. ; concrete, brick, and bituminous concrete, 41 per cent. The percentage of Federal Aid money spent on bituminous concrete roads was well under 5 per cent, of the whole amount. As the automobile density with reference to the population in the United States is about 300 per' cent, greater than in New Zealand, it will be seen that if a policy somewhat akin to that of the Bureau of Public Roads is followed by the Main Highways Board in this country, then only a moderate fraction of the proposed expenditure for a number of years will be for the high-class pavements. It would be as well to point out also that tho States in which, a considerable proportion of tho mileage of concrete roads has been laid down have an automobile density 500 per cent, greater than that of New Zealand. Suitable types of Road for New Zealand Main Highways. As mentioned in the previous section, the type of pavement to be chosen for any particular locality depends on local conditions, the most important of which are the existing traffic, and the possible future traffic after improvement. The future of the motor-vehicle in New Zealand can only be estimated by investigating the expansion that has taken place in the American States, as this Dominion per unit of population already possess twice as many motor-vehicles as England, which again is more advanced than any of the other European countries. The American States which have embarked on the most expensive concrete-road programmes have about 170 motor-vehicles per mile of declared main highway. New Zealand at the present time has about ten motor-vehicles per mile of main highway. Assuming in the next ten years a 500 per cent, increase (which would appear to provide a satisfactory margin), one can see that even ten years hence, if the American precedents are taken as any guide, the question of introducing concrete roads to any great extent on the main highways will scarcely warrant serious discussion. Estimates of the capability of various types of roads to take traffic economically in other countries vary to some extent, but there is sufficient information available to make it quite clear what typos should bo generally used in Now Zealand for some; considerable time. Tho following tabulation shows some comparative values by four various authorities : — Motor-vehicles per Day. 16 ft. gravel road .. .. . . .. .. .. .. 50-75 500 16 ft. gravel road, tar or bituminous surface .. .. 500* 660 500-700 2,000 16 ft. waterbound macadam with bituminous surfacing .. 1,000 1,000 1,500 2,500 16 ft. waterbound-macadam road .. .. . . .. . . 50 16 ft. bituminous penetration road. .. .. .. .. 1,550 .. 5,000 16 ft. asphaltic concrete .. .. .. .. .. 3,000 16 ft. concrete road .. .. .. .. ..2,000 5,000 * No loaded lorry to be over 8 tons in gross weight.