The draw of the U.S. 9 bridge, mile 2.6, at New Gretna, shall operate as follows:

(a) The drawspan must open on signal if at least six hours notice is given, except that public vessels of the United States must be passed as soon as possible.

(b) The owners of this bridge shall provide and keep in good legible condition clearance gauges for the draw span with figures not less than 12 inches high designed, installed and maintained in accordance with the provisions of § 118.160 of this chapter.