§ 43. Persons with whom contracts may be made. Nothing contained in this chapter shall be deemed, or be construed as intending to limit, or as limiting, in any manner, the discretion of the board of transportation, provided in the opinion of the board of estimate and the mayor, it is expedient, practicable and in the public interest to do so, to enter into contracts for construction, equipment, maintenance and operation with the same person, or for any one or more of such purposes with the same person or with different persons either in one contract or in separate contracts, and at any time or times.