U.S. Highway 18 (US 18) is the northernmost east–west United States Numbered Highway in the state of Iowa. As with all state highways in Iowa, it is maintained by the Iowa Department of Transportation. It enters the state by crossing the Big Sioux River between Inwood and Canton, South Dakota. It travels about 312 miles (502 km) and connects Spencer, Mason City, and Charles City. The highway leaves the state via the Marquette–Joliet Bridge over the Mississippi River at Marquette. Prior to becoming a U.S. Highway, the route US 18 follows was known as Primary Road No. 19 and the National Parks Pike.
US 18/US 218/Iowa 27 pass a wind farm near Charles City
US 18 crosses into Wisconsin via the Marquette–Joliet Bridge
US 18 passing through McGregor in 1975
Iowa Primary Highway System
The primary highway system makes up over 9,000 miles (14,000 km), approximately 8 percent of the U.S. state of Iowa's public road system. The Iowa Department of Transportation is responsible for the day-to-day maintenance of the primary highway system, which consists of Interstate Highways, United States Highways, and Iowa state highways. Currently, the longest primary highway is U.S. Highway 30 at 332 miles (534 km). The shortest highway is Interstate 129 at 0.27 miles (430 m).
A concrete Lincoln Highway route marker as seen at the Smithsonian National Museum. Few of these markers still exist along the route.
U.S. Highways in Iowa as designated in 1926
U.S. Route 34 near Chariton, a typical rural Iowa scene along Iowa's highways.
Lincoln Highway bridge in Tama
