In 1972, civil engineers in northern Illinois used 246,000 cubic yards of coal fly ash to construct the core of a 7,500-foot expressway embankment near Waukegan along US Route 41. ^[1] Long-term monitoring of the Waukegan project found no evidence of structural settlement, frost heave, or problems caused by rising groundwater. ^[2] In 2002, almost 300 tons of crushed glass were used as fill material for a 200-foot section of Idaho Highway 75 near Ketchum. ^[3] The Federal Highway Administration included the Waukegan project in its detailed user guidelines for highway construction. ^[4] The project demonstrated that fine ash from coal-fired power plants could replace traditional soil and aggregate used as backfill in highway construction. ^[5] The glass fill was placed in an 8-to-12-inch layer beneath the road surface during a $5.6 million highway reconstruction project. ^[6] The Federal Highway Administration states that properly sized and processed cullet can behave similarly to gravel or sand. ^[7] The glass material was sourced from the Ohio Gulch Recycling Center in the Wood River Valley. ^[8]