A barrier mechanism for providing selective access to a passageway on the floor of a lobby, room or pavilion. It utilizes a frame and carriage assembly thereon, a panel which is swivelable to selectively overlie and block the passageway, and an electric motor which powers the carriage assembly and moves the panel. A group of power components, including a driver operated by the motor and other linkages on the frame, provide simultaneous translating movement of the carriage assembly and panel and swiveling of the panel, synchronized to bring about a “wrap-around” effect to the latter. Optionally, the panel can be locked in either its blocking or its access position. Important safety features are incorporated in the mechanism, to prevent inadvertent injury to passageway personnel.