The Mayor shall appoint at least one but no more than two alternate Planning Board members, subject to approval by the Board of Trustees. The terms of the alternate members shall be three years, and no alternate member shall be appointed in the same year as another alternate member, except to fill the unexpired term of a vacancy. The Chairperson of the Planning Board may designate an alternate member to substitute for a regular member when such member is absent or unable to participate because of a conflict of interest on an application or matter before the Planning Board. Any alternate members shall attend all meetings of the Planning Board, shall sit with the regular members during the review of matters before the Board, and shall participate in all actions of the Board up to, but not including, voting on motions, resolutions and actions, unless they are substituting for a regular member.