Flexible Pavement Test Sections for Studying Pavement Design

It is a well-recognized fact that our pavement design procedures are inadequate in general and seriously lacking in many particulars. The fact that this statement can be applied on a county, state or national basis is little consolation to those in Indiana who must design and build pavements, for ever-changing traffic conditions, in such mileage and at such unit costs compared to the funds available that a working margin of safety is practically nonexistent. Although pavement design procedure went through an uneasy period in the 1920’s when increased volume and weight of traffic appeared to be damaging to highways then existing, changes in design of the pavement and the vehicle and, particularly, conversion to pneumatic tires alleviated the situation until in the early 1930’s the road system was considered structurally adequate. Commissioner McDonald o f the Bureau of Public Roads made a statement to this effect in 1931, and though the statement recently has been misapplied in some quarters, this fact does not detract from its value as repre­ senting conditions existing at the time it was made. The total thickness of the flexible pavements of this day was commonly determined by the general practice o f the area and frequently was a macadam type o f construction; either water-bound, bituminous pene­ trated or both. At that time, the volume and weight of traffic and the frequency of heavy axle loads were small compared to present conditions and pavement thicknesses determined by rule-of-thumb procedures were generally satisfactory. Beginning in 1940 the number of heavy axle loads per thousand vehicles began to rise sharply. By 1942 the intensity of heavy axle loads had tripled, and by 1948 the total number o f heavy axle loads was 18 times the number in the 1936-37 period. Also, by 1948 the total number of gross loads of 40,000 pounds or more was 12