Page:America's Highways 1776–1976.djvu/452

 In 1905, coal tar and crude oil were experimentally applied to recompacted macadam streets in Jackson, Tennessee. After nearly a year of observation, it showed that the coal tar had penetrated from 1 to 2 inches and maintained a hard smooth surface. However, the light crude oil used showed little permanent results. The heavier crudes showed nearly the same results as coal tar. Late in 1906, coal tar was used by Khode Island on a short section of the New York to Boston trunk highway in Charlestown in much the same method as building an ordinary macadam road. After the subgrade had been thoroughly rolled, the number one stone (1¼-inch to 2¼-inch diameter) was spread to a depth of 6 inches and rolled to 4 inches. Heated tar was then sprinkled on the first course with dippers. The number two stone (1½-inch to 1¼-inch diameter) was next mixed by hand with hot tar and spread to a depth of 3 inches on the first course and rolled to 2 inches. A thin coat of fine stone (passing ½-inch ring) was then spread on the surface and rolled into the number two course to fill up the voids and provide a smooth surface—1¼ gallons of the tar per square yard were used in all. As this method provided a stable hard surface, it was advocated by State engineers for use on first class highways.

Use of portland cement concrete pavement also was beginning to grow, as the steel drum tilting mixer came into use. The first rural concrete pavement, however, was not constructed until 1909 in Wayne County, Michigan.

In terms of new equipment and techniques, steel forms were being produced for concrete work and the gasoline engine came to construction work as the power unit for hoisting and excavation equipment, spelling doom for the steam engine. The diesel engine was also being developed and crawler tracks were being tried on tractors and cranes. A wooden-boomed excavator was rigged with a drag bucket in 1903, making this the forerunner of the drag-line. By 1907, a sheepsfoot roller was in use on embankment work on West Coast road construction. A rock crusher and elevator was mounted on a four-wheel truck in 1910 to become the first portable crushing and screening plant.

First graders ever used on highway construction work. Fixed with adjustable blades to provide the desired slope and section, graders were suited for fine grading and shaping.

Even though the first Federal Aid Road Act was not passed until 1916, in 1912, the Congress authorized funds for the improvement of post roads with the appropriation of $500,000, to be expended in rebuilding and upgrading roads used in the rural free delivery of mails.

An early roller compacting a roadbed.

The first of these road projects to be built was in Lauderdale County, Alabama, where approximately 30 miles of road was graded and surfaced with gravel at a total cost of nearly $28,000. One-third of the cost was paid with Federal funds and the remainder 446