The following are post roads:
(1) the waters of the United States, during the time the mail is carried thereon;
(2) railroads or parts of railroads and air routes in operation;
(3) canals, during the time the mail is carried thereon;
(4) public roads, highways, and toll roads during the time the mail is carried thereon; and
(5) letter-carrier routes established for the collection and delivery of mail.
(
Section effective July 1, 1971, pursuant to Resolution No. 71–9 of the Board of Governors. See section 15(a) of