§ 31. Municipal construction of railroads. It shall be the duty of the board of transportation to consider the routes, plans and specifications, if any, previously laid out and adopted by them or their predecessors, and for which the consents have been obtained referred to in section twenty-one of this chapter; and either to proceed with the construction of such railroad, and provide for the operation thereof, or to change and modify such routes, plans or specifications in such particulars as to such board may seem to be desirable, or from time to time and with or without reference to former routes or plans to adopt other or different or additional routes, plans and specifications for such railroad. In all cases in which any such change or modification shall be of such character as to require the consents thereto referred to in section twenty-one of this chapter and in all cases where other or different routes or general plans may have been so adopted, the board of transportation shall proceed to secure the consents required to be obtained by section twenty-one of this chapter. Prior to the time of the final grant of any franchise under the provisions of this chapter or the making of a contract for construction of any railroad under the provisions of this chapter, the board of transportation shall have power to rescind and revoke any resolution of such board or its predecessors adopting any routes or general plan for a railroad adopted by such board or its predecessors and, in the discretion of such board, in lieu thereof to adopt new routes and a general plan. Every such rescindment or revocation which shall have been made by such board of transportation or its predecessors shall be deemed to have been lawful and authorized by the rapid transit act, as the same was in effect on the twenty-third day of April, nineteen hundred.

b. As soon as such consents, where necessary, shall have been obtained for any railroad and the detailed plans and specifications have been prepared as provided in section twenty-two of this chapter, such board of transportation, for and in behalf of such city, may enter into a contract with any person, which in the opinion of such board shall be best qualified to fulfill and carry out such contract for the construction of such road, including such sub-surface structures as such board may include in the plans for such road under the authority of section twenty-two of this chapter, upon the routes and in accordance with the plans and specifications so adopted, for such sum of money, to be raised and paid out of the treasury of such city, as provided by this chapter, or to be contributed in part or in whole for the construction of such road by the contractor having the contract for the equipment and operation of such road as a consideration for the making of such contract for equipment and operation as provided by this chapter. Such contract for construction shall contain such terms and conditions, not inconsistent with the aforesaid plans and specifications, as such board shall determine to be best for the public interests. The sum of money to be paid for the construction of such road shall be separately stated in the contract from the sum to be paid for any sub-surface structures, the construction of which is provided for in such contract. Such board, in any case, may contract for the construction of the whole road, or all the roads provided for by such plans in a single contract, or, by separate contracts, executed from time to time, or at the same time, with one or more such persons, may provide for the construction of a part of such road or for the construction at first of two or more tracks over a part of such road and afterwards of one or more additional tracks over a part of such road as the necessities of such city and the increase of its population or the advantageous and economical performance of the work in the judgment of such board may require. In the alternative such board, in its discretion by separate contracts executed from time to time or at the same time, may contract with one or more persons for the performance of any kind of work or any portion of the work or for the furnishing of any material or for the performance of any labor necessary for or incidental to the construction of such road. In any case where any such contract which shall have been entered into provides that upon the happening of any event or default specified in such contract such board shall have the right and be entitled to take over and perform or complete or contract for the performance or completion of the work embraced in such contract or any part of such work, such board, upon the happening of any such event or default so specified in such contract, with the approval of the board of estimate and the mayor, also may employ such persons and purchase or hire such plant, tools, machinery, supplies and materials as may be necessary, and itself perform or complete the work embraced in such contract or any part of such work as in its judgment the public interests require.

c. The board of transportation, in the contract for a part of any such railroad, also may insert a provision that at a future time, upon the requirement of the board, the contractor shall construct the remainder or any part of the remainder of such road, as the growth of population or the interests of the city, in the judgment of the board, may require. Such board may insert in such contract provision for a method for fixing and ascertaining at such future time the amount to be paid to the contractor for such additional construction, and to the end of such ascertainment may provide for arbitration or for determination by court of the amount of such compensation, or of any other details of construction which shall not be prescribed in the contract, but which shall be deemed necessary or convenient by such board. If the public interest, in the opinion of the board, shall justify the provision, any such contract may provide that the construction of any section or portion of the railroad included in such contract, with the consent of such board, may be suspended during the term of operation of the railroad as provided in this section, or any part of such term. During such term or part of term there shall be available for use, in lieu of such portion of the road, a railroad or a portion or section thereof, which, with the railroad or portion of railroad constructed under such contract, shall form a continuous and convenient route.

d. Any such contract may be made for the construction of such road in sections, or for the construction of any section thereof. Except as otherwise provided in this chapter, every such contract shall specify when the construction of the railroad or the section thereof included therein shall be commenced in each case, and, in each case, the date of completion. The board of transportation may by any such contract determine when and how the work of construction of the railroad included therein shall proceed. The board may also provide for the equipment at public expense of such railroad in connection with the construction thereof, and may include in any contract for construction authorized by this chapter provision for the equipment, or any part thereof, of such railroad, but may make a separate contract for the whole or any part of such equipment with the constructing contractor or any other responsible persons. Any such contract, in lieu of requiring the contractor to provide equipment or any part thereof for generation or furnishing of motive power, may authorize the contractor to enter into a subcontract for purchase and delivery as required of motive power for operation of such railroad, provided such subcontract, as to the parties thereto, the sureties thereon and the terms thereof, shall be first approved by the board. In the alternative such contract may provide that the construction or completion of equipment, or any portion thereof, for generation or furnishing of motive power included in such contract, with the consent of the board, may be suspended during a period designated, provided that during such period there shall be available for use when required, in lieu of such equipment, motive power furnished to the contractor under and pursuant to the terms of a contract for the purchase of power, which contract shall, as to the parties thereto, the sureties thereon and the terms thereof, be first approved by the board. In case of the expiration or termination, of the contract for equipment, maintenance and operation of such road, as provided in this chapter, any subcontract for the furnishing of power may be terminated or taken over by the city without making any allowance or paying any amount to the contractor for or on account of any unexpired term of such subcontract.

e. Any railroad constructed by and at the expense of the city shall be and remain the absolute property of the city, and shall be and be deemed to be a part of the public streets of the city, to be used and enjoyed by the public subject to such reasonable rules and regulations as may be imposed and provided for by the board of transportation.