The federal government did in many situations buy or obtain rights of way for highways; at least, that was the written policy until Statehood.  But some State highways have gaps in them where the feds did not buy or obtain rights of way.  Also, many Alaska homesteaders worked for the federal road bureau and borrowed bureau equipment to put in roads; many of those roads are on the State road system, but there may not actually be legal rights for the public to use the roads.