Ariz. Rev. Stat. § 40-1126
An authority may contract for and cooperate with and may accept grants, contributions, or loans directly through the sale of securities or equipment, trust certificates, or otherwise, from the United States, or any department, instrumentality, or agency thereof, for the purpose of financing the acquisition, construction, improvement, maintenance and operation of transportation facilities and equipment or for the study and planning thereof, in accordance with any legislation which Congress may have heretofore adopted or may hereafter adopt, under which aid, assistance and cooperation may be furnished by the United States in the acquisition, construction, improvement, maintenance and operation or in the financing of the acquisition, construction, improvement, maintenance and operation of any such transit facility or equipment. An authority, in dealing with the federal government or agencies thereof, may waive any privilege or immunity if such action is deemed in the best interest of the authority.
A.R.S. § 40-1126