 Since before the primary highway system was created in 1920 , the Council Bluffs @-@ to @-@ Davenport , by way of Des Moines , corridor has always been important . Two roughly parallel auto trails , the Great White Way and the River @-@ to @-@ River Road , served cross @-@ state traffic . The two routes were merged into one route , the Whiteway Highway , in 1922 . Four years later , the Whiteway Highway would become US 32 . The US 32 designation was absorbed into an extended US 6 in 1931 . Previously , US 6 had existed only in the Northeastern United States . Within ten years , US 6 was the most @-@ traveled road in Iowa , with an average of " 1 @,@ 920 cars a day at any given rural point . " 
