Page:America's Highways 1776–1976.djvu/457

 By the 1920’s, crawler tractors were pulling scrapers and other equipment. This tractor could pull 5 scrapers at once, enabling these men to excavate and move material more efficiently.

An important program started by the BPR during this period was the “Production Cost Studies,” a management tool to promote efficient road construction operations. These studies on earth moving and concrete pavement construction produced practical applications. From the results of these studies, savings of from 25 to 35 percent were possible in earthwork by selecting the right number of appropriate pieces of equipment best suited to the particular job. The process applied to the concrete paving operations showed that production losses were mainly the result of the failure to provide appropriate hauling equipment in number and character to maintain the capacity of the concrete mixer. By careful elimination of such losses, astonishing increases of from 25 to 100 percent were made by Public Roads engineers in the output of working paving organizations. The most gratifying result, however, was the success that some contractors attained in nearly doubling their output by employing similar methods, and thereby permitting them to drastically reduce their next bids on concrete pavement items.

Another important development in earthwork was the ability to compact soil embankments. Early experiments showed that the amount of moisture in soil had a great influence on the degree of compaction that could be attained. This, of course, led to the use of moisture control methods of compaction and the development of the “Proctor” method of testing the compaction of soil embankments, a method which later became standard on highway embankments throughout the country.

The Public Roads engineers were actively working with various State highway departments and universities in cooperative investigations to develop suitable cheap roadway surfacing materials. At the University of Georgia, tests were underway on sand-clay. In Iowa and South Dakota tests were being run on methods of stabilization of soils with cement and lime. South Carolina was experimenting with bituminous applications to preserve earth roads. Investigations continued in Iowa on the tractive resistance of various types of highway surfaces. In Kansas, tests were being conducted to measure tire wear on various surfaces. In addition, the Bureau also was continuously making routine examinations of highway materials and coordinating the work of a large number of State and commercial laboratories making tests for the acceptance of materials on Federal-aid projects. The result of this work was a general improvement of all laboratories with the corresponding benefit to both Federal-aid and State highway construction projects.

A tractor-pulled grader maintaining a gravel-surfaced road in Minnesota. Self-propelled motor graders were introduced in the early 1920’s but were not widely used until much later. 451