The draw of the Conrail bridge, mile 2.8 at South River shall open on weekdays (exclusive of holidays) from December 1 through the last day of February if at least four hours notice is given. From March 1 through November 30, and December 1 through the last day of February on weekends and holidays the draw shall be maintained open to navigation except for closure to accommodate passage of a train. The draw shall be opened as soon as possible at all times for passage of a public vessel of the United States.