Last year''s full-depth recycling of a scenic road in Utah''s Zion National Park, incorporating foamed asphalt, shows how roads in environmentally sensitive areas can be reconstructed economically and with minimal impact on the ecology.

In the recent National Asphalt Pavement Association book, Paving the Way: Asphalt in America, author Dan McNichol cites Stephen Mather, the first director of the National Park Service, for his efforts "to make the parks accessible to the people" by constructing and upgrading their roads.

Beginning with the Going to the Sun road project in Glacier National Park in the mid-1920s, and up to the outbreak of World War II, roads were constructed in many parks, including Yosemite, Grand Canyon, Yellowstone, and Zion. In each case, the NPS insisted that the road must "lie lightly on the land," meaning that the roadway design had to consider aesthetics and fit into the natural surroundings.

But the popularity of our national parks has grown tremendously in recent years because of the awesome beauty of these treasures and the excellent access available. However, increased traffic volumes, including a high percentage of larger trucks and RVs, far exceed the original pavement structural designs and have taken their toll on the park roads.

According to the National Parks Conservation Association, 65 percent of the 5,000 miles of paved roads in U.S. national parks are in poor to fair condition. Now stakeholders must ask, "How should these failed roads be rehabilitated in a cost-effective but environmentally sustainable way?" Adding several layers of HMA would not economically or aesthetically solve the inadequate structural strength of the pavement. Instead, the FHWA''s Federal Lands Highway Division has turned to full-depth reclamation (FDR) with foamed asphalt as the pavement rehabilitation method of choice.

In FDR, the entire thickness of an asphalt pavement is pulverized in-place and blended with a specified amount of the underlying granular road base materials. To this reclaimed material is added a combination of foamed asphalt and cement stabilizing agents. Just enough asphalt and cement are added to produce a strong yet flexible road base. This process has been used successfully throughout the world and in the United States, including all Federal Lands Highway Divisions, on roads in Canyon de Chelly National Monument, Ariz.; Rocky Mountain National Park, Colo.; Helena National Forest, Mont.; and Delaware Water Gap National Recreation Area, N.J.

Use of foamed asphalt in Zion National Park minimized the disruption of tourist traffic; eliminated the noise, dust and commotion of pavement demolition and "ant train" of haul trucks removing demolition materials and replacement with virgin base; and saved countless gallons of expensive gasoline or diesel fuel used by those trucks, as well as autos caught in construction-related congestion.