- The Commissioner, when authorised by the corporation in this behalf, may agree -

(a) with any person to adopt and maintain any existing or projected bridge, via duct or arch, and the approaches thereto, and may accordingly adopt and maintain such bridge, via duct or arch and approaches as parts of public streets, or as property vesting in the corporation; or

(b) for the construction or alteration of any such bridge, via duct or arch or for the purchase or acquisition of any adjoining land required for the foundation and support thereof or for the approaches thereto, either entirely at the expenses of such person or partly at the expense of such person and partly at the expense of the corporation.