14 C.F.R. § 121.95
(a) Approved routes and route segments over U.S. Federal airways or foreign airways (and advisory routes in the case of certificate holders conducting flag operations) have a width equal to the designated width of those airways or routes. Whenever the Administrator finds it necessary to determine the width of other approved routes, he considers the following:
[Docket 6258, 29 FR 19194, Dec. 31, 1964, as amended by Amdt. 121-253, 61 FR 2610, Jan. 26, 1996]