Funds made available to carry out this section shall be available for obligation in the same manner as if such funds were apportioned under chapter 1 of title 23, United States Code; except that such funds shall not be transferable to other agencies and shall remain available until expended and the Federal share of the cost of a Project of National and Regional Significance shall be as provided in section 505.13 .
23 C.F.R. § 505.17