Governmental DOTs (Departments of Transportation) or regional water authorities often provide free PKT files to ensure consultants are using approved designs. Check the "CADD Standards" page of your local DOT website. How to Import and Use a PKT File in Civil 3D
A subassembly pkt file is a package file used in Autodesk Civil 3D to create and manage subassemblies, which are reusable components used to build corridors, intersections, and other infrastructure designs. civil 3d subassembly pkt download free