The Massachusetts Department of Transportation is scheduled to hold a design public hearing at 7 p.m. Thursday in the Memorial Hall Library, 2 North Main St., regarding the proposed replacement of the North Main Street bridge over the MBTA railroad. The project would replace the span’s superstructure and partially replace its substructures. The bridge also would be raised slightly to help accommodate modern train requirements and new steel rails would be installed. During construction, two lanes of traffic would be maintained. The project would require a secure right-of-way; therefore, the state transportation department’s policy concerning land acquisitions will be discussed at the hearing. Written comments may be submitted to Thomas F. Broderick, Chief Engineer, MassDOT, 10 Park Plaza, Boston, MA 02116, Attention: Accelerated Bridge Program, Project File No. 601986, within 10 days of the public hearing.