There are 223,000 miles of heavily trafficked roads in the United States. They slice through landscapes, connecting communities and economies, but also bisecting and contaminating nature. Transportation accounts for more than 25% of total U.S. emissions, and busy roads can produce up to five times the levels of pollutants (copper, zinc, chloride, nitrogen, and phosphorus) than rural roads. In short, roads are energy-intensive, dirty structures—but we can’t live without them. While scientists are working on…