What is Section 4(f) of the Department of Transportation Act of 1966?

Section 4(f) refers to the original section within the United States Department of Transportation (DOT) Act of 1966 (49 U.S.C. Section 303(c); 23 U.S.C. Section 138). The DOT Act was enacted to ensure that transportation plans and programs include measures to maintain or enhance the natural beauty of publicly owned public parks, recreation areas, wildlife/waterfowl refuges, and historic sites of local, state, or national significance transversed by highways.

Source
Interagency Wild & Scenic Rivers Council