In 2024, Arizona put 100% recycled glass beneath a 23-mile interstate expansion; the unusual material helped protect 19 sets of existing highway culverts

When Arizona widened Interstate 17, engineers faced a problem that drivers would never notice. Beneath the planned expansion were 19 sets of existing culverts, built when the highway was narrower. Adding heavy soil and rock could put too much pressure on them. So engineers looked for something lighter. They used foam glass made from 100% recycled glass at 19 locations along the 23-mile project.