23 U.S.C. 202(b)(3)(A) provides the basis for the funding formula and its transition into use. The annual TTP funding amount available for distribution is determined as follows:
(a) The following set-asides are applied to the Tribal transportation program before the determination of final Tribal shares:
(1) Tribal transportation planning (23 U.S.C. 202(c));
(2) Tribal transportation facility bridges (23 U.S.C. 202(d));
(3) Tribal safety (23 U.S.C 202(e));
(4) Administrative expenses (23 U.S.C 202(a)(6)); and
(5) Tribal supplemental program (23 U.S.C. 202(b)(3)(C)).
(b) After deducting the set asides identified in paragraph (a) of this section, on October 1 of each fiscal year, the Secretaries will distribute the remainder authorized to be appropriated for the TTP among Indian Tribes as follows:
(1) For fiscal year 2016 and thereafter:
(i) For each Indian Tribe, 20 percent of the total relative need distribution factor and population adjustment factor as determined by the Tribal Transportation Allocation Methodology (see 25 CFR 170 dated July 19, 2004)) for the fiscal year 2011 funding amount made available to that Indian Tribe; and
(2) [Reserved]