33 CFR § 117.591 - Charles River and its tributaries.
(a) The following requirements apply to all bridges across the Charles River and it's tributaries:
(1) Public vessels of the United States, state or local vessels used for public safety, and vessels in distress shall be passed through the draw of each bridge as soon as possible without delay at any time. The opening signal from these vessels is four or more short blasts of a whistle or horn, or a radio request.
(2) The owners of these bridges shall provide and keep in good legible condition clearance gauges for each draw with figures not less than 12 inches high designed, installed and maintained according to the provisions of § 118.160 of this chapter.
(3) Trains and locomotives shall be controlled so that any delay in opening the draw span shall not exceed ten minutes. However, if a train moving toward the bridge has crossed the home signal for the bridge before the signal requesting opening of the bridge is given, that train may continue across the bridge and must clear the bridge interlocks before stopping.
(4) Except as provided in paragraph (b) through (f) of this section, the draws shall open on signal.
(b) The draw of the Massachusetts Bay Transportation Authority (MBTA/Amtrak Bridge, mile 0.8, at Boston, shall open on signal; except that from 6:15 a.m. to 9:10 a.m. and 4:15 p.m. to 6:30 p.m., Monday through Friday, except holidays, the draw need not be opened for the passage of vessels, except as stated in paragraph (a)(1) of this section.
(c) The draw of the Massachusetts Bay Transportation Authority (East Cambridge Viaduct) railroad Bridge, mile 1.0 at Boston, need not be opened for the passage of vessels. However, the operating machinery of the draw shall be maintained in an operable condition.
(d) The draw of the Massachusetts Department of Transportation (Craigie) Bridge, mile 1.0 at Boston, shall operate as follows:
(1) Open on signal; except that from 6:15 a.m. to 9:10 a.m. and 3:15 p.m. to 6:30 p.m., Monday through Friday, except holidays, the draw need not open for the passage of vessels, except as stated in paragraph (a)(1) of this section.
(2) From December 1 to March 31, the draw shall open on signal after a 24 hour advance notice is given.
(3) From midnight to 8 a.m., April, May, October, and November, the draw shall open on signal after at least an eight-hour advance notice is given.
(e) The draws of the bridges across Broad Canal, mile 0.0, need not open for the passage of vessels. However, the draws shall be returned to operable condition within one year after notification by the District Commander to do so.