Va. Code § 33.2-2504
A majority of the Authority, which majority shall include at least a majority of the representatives of the counties and cities embraced by the Authority, shall constitute a quorum. Decisions of the Authority shall require a quorum and shall be in accordance with voting procedures established by the Authority. In all cases, decisions of the Authority shall require the affirmative vote of two-thirds of the members of the Authority present and voting and two-thirds of the representatives of the counties and cities embraced by the Authority who are present and voting and whose counties and cities include at least two-thirds of the population embraced by the Authority; however, no motion to fund a specific facility or service shall fail because of this population criterion if such facility or service is not located or to be located or provided or to be provided within the county or city whose representative's sole negative vote caused the facility or service to fail to meet the population criterion. The population of counties and cities embraced by the Authority shall be the population as determined by the most recently preceding decennial census, except that once the population estimates for July 1 of the fifth year are made available then the population of each county and city shall be adjusted on the basis of population estimates made by the Weldon Cooper Center for Public Service of the University of Virginia.
Va. Code § 33.2-2504