Page:America's Highways 1776–1976.djvu/465

 The array of road construction equipment that was available at this time was huge and diverse, but every unit was developed in an orderly fashion to fill a definite need.

Significant advances in paving equipment were started. In 1955, electronic controls were put into use in concrete batch plants, simplifying and giving better control over batching. The triple-drum concrete paver, which could produce 125 batches per hour compared to 87 batches for the dual-drum, was introduced in 1959. Central-plant mixing with hauling by agitator trucks was used on large concrete paving projects. Transit mixers were widely used in urban paving and bridge work. Slipform pavers became widely accepted on highway work. Spreading and finishing equipment were developed to do a faster, better job. The use of central-plant mixing and slipform paving methods made possible some astonishing achievements in concrete pavement. Some road contractors reached the production rate of paving more than a mile per day of 24-foot wide, 9-inch thick Portland cement concrete pavement with this type modern equipment. This led to the “Mile-A-Day Club,” sponsored by the American Concrete Paving Association. In 1973, one contractor set a new record by paving 4.7 miles of 8-inch thick, 24-foot wide concrete pavement in a 23-hour period—14,853 cubic yards of concrete.

In the early sixties, automatic slope and grade controls for asphalt paver screeds were developed. Rolling equipment for bituminous pavements showed little apparent change over the years, but in reality improvements were developed for these machines during this period which made them faster, more productive, and easier to operate.

Other innovative developments included a helicopter designed to hoist and haul a 6-ton payload for construction work in inaccessible areas, and a vibratory sonic pile driver that could drive and pull piling at a small fraction of the time needed with conventional equipment.

In 1958, there were over 12,000 Federal-aid highway projects awarded at a total cost of about $3.5 billion to build or improve nearly 34,000 miles of roads. In 1964, approximately 7,000 Federal-aid projects were awarded at a total value of about $4 billion, corresponding to 18,300 miles of roads. The average size contract in 1958 was almost $300,000 and in 1964 was about $560,000—nearly doubled—while the total annual miles dropped. Obviously the trend was to shorter, more costly projects. In general, the longer rural, less costly Interstate projects were built first with the more costly and shorter urban projects following.

The high degree of mechanization of highway construction activity enabled construction labor to increase production greatly while reducing the number of man-hours required per mile of highway construction. The cost of highway construction over the years, in fact, has risen quite slowly as compared to the cost of labor and materials.

The paving train’s screw spreader.

By 1964 the Interstate program was in full swing. While highway mileage accomplishment for the Interstate was still the main goal, attention was focusing on other aspects such as highway safety, highway beautification, and consideration of wildlife and recreation areas, as well as historic sites. Environmentalists and ecologists were instrumental in keeping environmental concerns, potentially affected by construction, at a high level of consciousness among highway builders. New construction procedures were developed whereby detailed programs were implemented in order to reduce to a minimum the soil erosion during the construction process, and several States were investigating improved methods of sediment control for future highway construction use.

Studies were undertaken to investigate new equipment and other means to control noise and air 459