COST OF STRENGTHENING.

Timaru Herald, Volume CXXXVII, Issue 19483, 6 May 1933, Page 12

COST OF STRENGTHENING.

In order to show how much more it would cost to construct adequate strength into the road for the various weight-classes of trucks, Mr. Kelly analysed figures compiled in Pennsylvania, which has 13,300 miles of main read and a total register of 1,780,919 vehicles, of which 96 per cent, are passenger cars or small trucks of under one ton capacity. Only 4 per cent, are trucks of a capacity of over one ton, and “in our study,” said Mr. Kelly,

“these will have to bear the extra cost entailed by strengthening the highways to carry them.” From the figures he subsequently gives, Mr. Kelly finds that “a simple way to show the extra cost of heavier vehicles in general is to say that by adding only 15 per cent, to the construction cost of the highway, as it would be designed in actual practice to carry passenger cars and light trucks and withstand weather effects, it is

made adequate for vehicles up to and including seven and one-half tons capacity.” To the question of the effect on the highway surface of the heavy loads carried by trucks, Mr. Kelly said: “The question reflects an all too prevalent misunderstanding. The fact is that so far as surface wear is concerned, no one really knows how long a modern, well-constructed, high-type pavement will last. In reaction between the speeding tire and the pavement, it is the tire that wears out, not the pavement. The painted lines on the surface of any heavily travelled modern highway, such as those used to indicate railroad crossings, will last a year despite the constant rolling over them of hundreds of thousands of rubber tires.

“Experiments made in Washington have shown that even solid tires produce no measurable wear on a properly constructed pavement—not even after 300,000 passages of a solid the always following in exactly the same track, and supporting one andcne-half tons at a seed of twenty-two miles an hour. This load represented 600 pounds per inch width of tire, which was the equivalent of 16,000 pounds axle-load on a fourteen-inch solid tire. Since

ply back and forth along the highways and trailers are not unknown.

These changes mean that highway engineers have a never-ending task in eliminating road hazards which contribute to motor vehicle accidents. The street system of towns and the highway system in the country should be studied constantly with the view to determining where traffic hazards exist and the best means of eliminating them, or giving protection.