The test road consisted of about 7 miles of two-lane pavements, half of concrete and half bituminous. The roadways included 16 short-span bridges. There were 836 separate test sections located in six loops which varied in length from 2,000 to 6,600 feet. The test sections had selected factorial combinations of surface, base, and subbase thicknesses. Axle loads differed on each loop and varied from 2,000-pound single to 48,000-pound tandem; truck trailer units were included. Full-scale tests started in November 1958 and terminated in November 1960. A total of 1,114,000 axle loads had been applied to the pavements and bridges surviving at the last date.
The project produced a reservoir of facts long needed for the development of a more refined and scientific design of pavements and short bridges.[N 1]
The test data well established the desired relations of pavement structural designs (component thicknesses) and loadings (magnitude and frequency of axle loads). These findings were developed in the form of equations and graphs that showed the effects of particular variables on pavement performance. These soon were incorporated by AASHO and others into pavement design guides and manuals. The concept and use of a “serviceability index” to define pavement performance was a major item. And the data on equivalencies of single- and tandem-axle loads for the same pavement performance was a high-use product. Also important were: a method to predict pavement performance from measurements of deflections and strains; and data on the reduction of surface skid resistance.
The test bridge findings largely verified design predictions of deflection and strain. The dynamic studies resulted in the formulation of new theoretical concepts for analytical evaluation of stresses and deflections from moving vehicles.
- ↑ The extensive technical data and findings are recorded in seven Highway Research Board Special Reports Series 61, and Special Report 73.
Construction and Maintenance
Production Costs
The construction of highways in the early stages of our country’s development involved mostly hand labor and draft horse or mule power. Formal organization and production efficiency were items unheard of, and the pace of construction depended, for the most part, on the forcefulness and ingenuity of the foreman. Later, as mechanized methods started to supplement the man and mule power method, the need for systematic organization increased. Early Public Roads activities in this area concentrated mostly on object lessons gained in test road construction.
In the early 1920’s, the Production Cost Study Program was initiated by the Bureau to assist the highway industry in analyzing its various operations regarding time utilization and operational efficiency of equipment used in construction. This program, led by T. Warren Allen, served two purposes: (1) To assist the contractor by direct time-motion studies on their operations, expressed in terms of production rates and costs, pointing out observed inefficiencies and measures as to how he might improve on his operations; and (2) to train junior engineers in Public Roads by direct exposure to the practicalities of construction equipment operations and the overall process of building a highway. This program continued until 1936.
There were 16 short-span bridges on the AASHO road test to determine deflection and strain on bridges from heavy loads.
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