The powers of the local district created in accordance with this chapter shall be exercised by a commission composed of four of the elected members of each of the boards of supervisors of the counties in which it is located, appointed by their respective boards of supervisors. The Chairman of the Commonwealth Transportation Board, or his designee, shall be an ex officio member of the commission. The members of the commission shall elect one of their number chairman. The chairman may or may not be the chairman or presiding officer of a board of supervisors. In addition, commission members, with the advice of the district advisory board, shall elect a secretary and treasurer, who may or may not be a member or employee of a board of supervisors or other governmental body represented on the commission. The offices of secretary and treasurer may be combined. A majority of commission members shall constitute a quorum, and the vote of a majority of the commission membership shall be necessary for any action taken by the commission. No vacancy in the membership of the commission shall impair the right of a majority of the members to form a quorum or to exercise all of its rights, powers, and duties. The 1990 amendments to the provisions of this paragraph shall not be effective for the Route 28 Primary Highway Transportation Improvement District until such time as the special tax revenues from the District exceed the total debt service on the bonds issued pursuant to Chapter 676 of the 1988 Acts of Assembly for three consecutive years.