23 U.S.C. § 323 — Donations and credits

(a) Donations of Property Being Acquired. If the government is acquiring someone's real property for a project^* under this title, that person can still choose to donate the property, part of it, or the payment for it, to a federal agency, a state^*, a state agency, or a local government. This is allowed as long as the person was first fully told of the right to receive just compensation.
(b) Credit for Acquired Lands.
(1) In general. A state's share of a highway^* project's cost (funded from the Highway Trust Fund, other than the Mass Transit Account) can be credited by the fair market value of land that: (A) the state or a local government lawfully obtained; (B) is built into the project; (C) is not land described in section 138; and (D) the Secretary^* decides will not affect the project's environmental review, including the decision to build it, considering alternatives, or picking the location.
(2) Setting fair market value. The Secretary decides how to set the fair market value of credited land, except: (A) that value cannot include any increase or decrease in the land's worth caused by the project itself; and (B) the value must be set as of the earlier of the date the donation takes effect or the date the state gets equitable title to the land.
(3) Limit on applicability. This credit rule does not apply to donations made by a federal agency.
(4) Limit on credit amount. A state's credit cannot exceed the state's matching share for the project.
(c) Credit for Donations of Funds, Materials, or Services. A person can donate money, materials, or services to a project eligible under this title. A local government can donate money, materials, or services performed by its own employees. If the federal government and the state split a project's cost, any donated funds, or the fair market value of donated materials or services, that the state transportation department^* accepts and uses in the project get credited against the state's share.
(d) Procedures. A gift or donation under (a) can happen any time while the project is being developed. Any document signed as part of the donation, before an environmental document required by the National Environmental Policy Act of 1969 (42 U.S.C. 4321 et seq.) is approved, must clearly state that: (1) all alternatives to the proposed route will still be studied under that Act; (2) acquiring the property under this section will not affect the project's environmental review, including the decision to build it or where to put it; and (3) if the route chosen after any required public hearings and the completed environmental document does not need the donated property, the property goes back to the donor or the donor's successors.