Walking on broken glass is probably a bad idea, but driving
over broken glass might be a good idea if the glass is used as fill under the
road. Clint Stennett, an Idaho state senator from Ketchum, had the idea that
waste glass piling up at the Ohio Gulch Recycling Center in the Wood River
Valley could be put to good use under nearby Idaho Highway 75.

“He was aware that there was glass that was being
sorted out very near to the project,” Devin Rigby, district engineer for
the Idaho Transportation Department, told Roads & Bridges. “He came
to us and said, ‘Can we incorporate that somewhere into the
project?’”

Stennett and Rigby appeared at the Highway 75 jobsite on
April 22, Earth Day, to answer questions about the use of the recycled glass. They
didn’t plan the glass to be placed on Earth Day, according to Rigby, it
just worked out that way.

The crushed glass fill is part of a $5.6 million, federally
funded project driven by the need to replace a narrow three-span bridge over
the Big Wood River. The new Greenhorn Bridge will be a two-span bridge with
prestressed concrete beams and a total length of 178 ft. It will carry three
lanes of traffic, with the capacity to expand to four lanes in the future.

The roadbed reconstruction covers about 1 mile on the south
end of the bridge and about 0.8 miles on the north end. Almost 300 tons of
crushed glass was used to compose 8-12 in. of fill along a 200 ft stretch of
the new roadway. Over that will go about 4 ft of borrow, made up of the
alluvial granular material typical of the geographic area, followed by a
3?4-in. base of crushed rock and 4?10 ft of asphalt.

The recycled glass was donated to the project by Southern
Idaho Solid Waste Recycling, Ketchum.

“We put the glass in, rolled it with a Cat [dozer] and
a roller and made sure that it was all broken up,” said Rigby. “It
compacts very much like any kind of a stone material; it’s just brittle.

“We anticipate using it again in the valley where we
have fill,” he continued. If Idaho wanted to use glass as a base
material, though, the glass would need a significant amount of processing to
clean it and make it meet grade specifications. The processing would probably
make glass prohibitively expensive compared with rock aggregate, which is
abundant in this area of Idaho.

Terry Schultz, director of Southern Idaho Solid Waste,
offered the Idaho Transportation Department more crushed glass in the future.
His organization has the ability to amass about 400-500 tons per year.
Otherwise the glass probably would be used to fill voids in a local landfill.

Ketchum (pop. 2,500) and its neighboring town of Hailey
(pop. 3,700) are located in a resort area known as Sun Valley. They are not big
population centers, yet an average of 15,000 cars per day cross the Greenhorn
Bridge on Highway 75 connecting them.

The reconstruction project also includes making safety
improvements to the intersection of Idaho 75 and Greenhorn and East Fork roads,
installing a traffic signal there and constructing a bike and pedestrian tunnel
near East Fork Road.

Highway 75 reconstruction started in spring 2001 and is
scheduled for completion this August.