Whenever any local road is found to cross the Natchez Trace Highway at a point which is not a parkway entrance, as defined by the national park service of the U. S. Department of the Interior, the board of supervisors of the county in which such road lies is hereby authorized to abandon that part of such road which crosses the Natchez Trace highway and parkway, and to relocate it so that said local road will connect with said Natchez Trace Highway at a fixed parkway entrance.