Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 160, § 138

Every railroad corporation shall cause a bell of at least thirty-five pounds in weight, and a whistle, to be placed on each locomotive engine passing upon its railroad;  and such bell shall be rung or at least three separate and distinct blasts of such whistle sounded at the distance of at least eighty rods from the place where the railroad crosses upon the same level any public way or traveled place over which a signboard is required to be maintained as provided in sections one hundred and forty and one hundred and forty-one;  and such bell shall be rung or such whistle sounded continuously or alternately until the engine has crossed such way or traveled place.  This section shall not affect the authority conferred upon the department by the following section.