Page:America's Highways 1776–1976.djvu/466

 during the construction process. The dryer-drum process for hot-mix asphalt plants and better mufflers for heavy equipment were developed in an effort to reduce or eliminate these types of pollution.



There was an increased emphasis on highway safety. New safety devices were built into new highways, such as sign posts that broke upon impact, safer guardrails, and crash cushions which absorbed the shock of a collision with fixed structural elements.

Activities on construction projects were also changing. Construction contractors in some States were being required to furnish completely equipped laboratories and do their own surveying and layout staking, jobs which had previously been done by State highway departments. More States were using aerial photography and new data processing procedures to speed up monthly estimates.

The highway construction industry developed a greater awareness of public need and good public relations. Soil erosion prevention and other environmental and ecological aspects became integral parts of construction practices. Ways were studied to help the construction labor force also. Where possible, activities such as winter concreting techniques were developed to help extend the construction season and to give workers more yearly income, and occupational safety measures were adopted to improve the working conditions for the construction work force.

A slip form paver eliminates the need for setting steel forms, since the forms move along with the paving machine. A relatively stiff concrete is used so that, by the time the machine passes on, the concrete will hold its shape. 460