You made me curious: https://pubs.usgs.gov/fs/2006/3127/2006-3127.pdf https://pubs.usgs.gov/fs/2006/3127/2006-3127.pdf There is almost 4 million miles (6.5 mil

You made me curious: https://pubs.usgs.gov/fs/2006/3127/2006-3127.pdf https://pubs.usgs.gov/fs/2006/3127/2006-3127.pdf There is almost 4 million miles (6.5 million kilometers) of roads in the United States, with just over 45,000 miles [73,000 kilometers (km)] composing the Interstate Highway System (fig. 2) (Federal Highway Administration, 2004). The total distance of U.S. roads combined could circle the Earth at the equator 160 times; the interstate highways, almost two times. The analysis shows that a total of approximately 1.5 billion metric tons (Gt) of aggregates, 35 million metric tons (Mt) of asphalt, 48 Mt of cement, and 6 Mt of steel is in place in inter- state highways. These estimates illustrate the large quantities of these materials used in the Interstate Highway System. This doesn't translate exactly to how much surface is covered, but I know locally all the highways are concrete. Also, placing sensors in 4M miles of roads is no small task.