N.J. Stat. § 48:12-54
Every company operating on a fixed track or tracks, freight or passenger trains or cars, shall provide protection to pedestrians and the traveling public at every crossing of its tracks by any public road. Such protection may be in the form of safety gates, flagmen, electric bell, electric signs or other recognized system of alarm or protection approved by the Board of Public Utility Commissioners.
When several crossings lie so close together that an audible signal at one crossing may be sufficiently heard at others near it, such crossings may be protected by such device or signals as will sufficiently protect all crossings in the group.
When on any line or part thereof all traffic is discontinued for any part of the night, no crossing guards need be operated while traffic is so discontinued.
This section shall not apply to street car lines or tracks used principally for street car purposes.
The provisions of this section shall be construed to be mandatory and shall be operative without order or direction of the board.
N.J.S. § 48:12-54