D.C. Code § 9-1101.01
The Mayor is authorized to enter into such agreements with the States of Maryland and Virginia and with political subdivisions of such States as may be necessary to develop a continuing comprehensive transportation planning process for the National Capital region for the purpose of complying with the requirements of §134 of Title 23, United States Code , except that no such agreement shall require the District of Columbia to pay more than its pro rata share of the costs of such planning process. In developing such transportation planning process the Mayor shall consult and cooperate with the National Capital Planning Commission and the National Capital Regional Planning Council. For the purpose of this section, the term "National Capital region" shall have the same meaning as is given it in § 1-1401.
D.C. Code § 9-1101.01