 U.S. Highway 30 ( US 30 ) is a major east – west U.S. Highway which spans 330 miles ( 530 km ) across the state of Iowa . It is the longest primary highway in the state and is maintained by the Iowa Department of Transportation ( Iowa DOT ) . The route in Iowa begins at the Missouri River crossing at Blair , Nebraska , and ends at the Mississippi River crossing at Clinton . Along the way , it serves Denison and Carroll in western Iowa , Boone , Ames , and Marshalltown in central Iowa , and Tama , Cedar Rapids , and DeWitt in eastern Iowa . Cutting across the central portion of the state , US 30 runs within close proximity of the Union Pacific Railroad 's Overland Route for its entire length . 
